(CNN) — Ayda Zugay isn't someone who normally likes to save things.
The walls of her Boston home are bare. She keeps a small bag packed with essential items in case she ever needs to leave quickly.
But for more than two decades, she's held onto an envelope that she hopes will help her unravel a mystery.
Zugay says she was a nearly 12-year-old refugee fleeing the former Yugoslavia with her older sister when a stranger handed them the envelope on a flight to the United States in 1999. The woman made them promise not to open it until they got off the plane.
The girls were later shocked to discover dangly earrings and a $100 bill inside.
A note scribbled on the outside of the envelope is signed with only a first name — Tracy. And for almost a decade, Zugay says she's been trying to find her.
She wants Tracy to know how much the gift meant. She imagines that to Tracy, or to others hearing the story, the envelope might seem like a small gesture.
But Zugay says that to her and her sister, who was 17 at the time, it was so much more than a momentary act of generosity.
That money, she says, helped feed them for an entire summer while the two girls scraped by staying with their brother, who was a college student in Iowa. And it's still shaping the way both sisters live their lives 23 years later.
Zugay has looked at the envelope for clues, chased down leads, dealt with doubts and hit dead ends. She's reached out to hotels, airlines and tour companies. She's talked with reporters and posted on Reddit.
But so far, she says she hasn't found Tracy. So she's trying to cast a wider net.
"I want to be able to find Tracy to thank her for her generosity, for her kindness, for her empathy, and for welcoming my sister and I," Zugay says, looking toward the camera as music plays in the background. "I was wondering if you could help me find her. Have you ever heard a family member or a friend or anyone share a story that's similar to this?"
It's a story that Zugay's told many times. But she still doesn't know how it ends.
In a video several refugee advocacy organizations are sharing on social media, Ayda Zugay asks for help finding the woman behind the envelope and its welcoming message.
From Refugees International/Twitter
Tracy's note on the outside of the envelope is written in cursive "to the girls from Yugoslavia."
“I am so sorry that the bombing of your country has caused your family any problems. I hope your stay in America will be a safe and happy one for you — Welcome to America — please use this to help you here. A friend from the plane — TRACY ”
It appears to be scrawled on a piece of hotel stationery -- possibly from somewhere she'd been staying. In the upper left-hand corner, "Holiday Inn Garden Court" is printed in blue.
The envelope itself isn't the only thing Zugay has to go on. She says she also knows a few other details from the flight -- some from her own recollections, and some details that her sister shared.
The Tracy who gave them the envelope was traveling with a friend, Zugay says, and she thinks that friend's name was also Tracy.
To Zugay, they appeared to be in their late 30s or early 40s. One was a brunette with a ponytail. The other had mid-length blonde hair. Both women toted tennis rackets they placed in the airplane's overhead bin. They spoke about playing tennis in Paris. And Zugay thinks they may have lived in Minnesota, possibly within a few hours of the Minneapolis-Saint Paul International Airport.
She remembers helping the women with knitting. Zugay didn't speak English at the time, but her older sister was able to carry on more of a conversation.
In her recent video, this is how Zugay describes who she imagines Tracy to be based on the clues she has:
"Tracy, by this time, would be a middle aged or an older woman who is amazing at tennis and had traveled for it in the past. She would have flown from Paris, where she stayed at a Holiday Inn and where she played tennis, to Amsterdam, where we met on that flight. She would have flown from Amsterdam to Minnesota, and this would have been on May 31, 1999."
This childhood photo of Ayda Zugay and her sister, Vanja, was taken after they came to the United States.
Courtesy Ayda Zugay
Zugay still remembers how she felt the first time she read the message on the envelope.
She noticed how the word "safe" was underlined.
"It was the first time that I felt, like, relief. This is a safe place, and we can build a future here," she says. "I think that's why the letter really resonated with me at that time, because we went from like this drastic horror into this beautiful act of kindness."
Her sister, Vanja Contino, doesn't recall many details from the flight itself. But she says she remembers the moment when they opened the envelope and found $100 inside.
"We both just looked at each other, me and my sister, and just hugged each other," she says. "Because that's all we had. ... And it was just amazing that somebody was willing to spend that kind of money on us."
Zugay says the gift was surprising in their early days in America, but it has only become more so with the passage of time.
"On the outside of the envelope was an amazing message of welcome," Zugay says in her recent video. "I treasure this because as time goes by, I've experienced that in most spaces, welcomes like this are very uncommon."
She'll never forget this act of generosity. But she has so many other memories, too -- stories that are painful for her to tell, about what it was like to begin her life in America.
Like the woman who once refused to accept the rolls of coins she and her sister tried to use to pay for something at a store, telling them didn't belong here.
Like the people who told her she should self-deport after Mitt Romney used the term during a 2012 debate.
Like those she's heard making unfair judgments about whether certain immigrants deserve to be in America.
Experiences like that have been so scarring, Zugay says, that for years she didn't like to talk about being a refugee. She took accent reduction classes and did everything she could to blend in.
"I just tried to erase my entire identity in order to feel accepted," she says, "only to realize that was never going to happen."
To Zugay, Tracy's note is a "diamond in the dark" -- and that's a big reason why she's kept it, and why she keeps looking for the woman who wrote it.
Zugay says she renews her search for Tracy every year around Memorial Day, the anniversary of when she and her sister arrived in the United States. Thanksgiving is another time when she often starts scouring for clues again. The annual celebration of gratitude, she says, makes her reflect on how that moment of kindness shaped her life.
"I've been trying to do this every Memorial Day and every Thanksgiving, trying to search, look online, reach out to different people and try different strategies," Zugay says.
With each attempt comes a mix of emotions.
"It definitely is hard to go back in time and live through these experiences again," she says.
“On the outside of the envelope was an amazing message of welcome. I treasure this because as time goes by, I've experienced that in most spaces, welcomes like this are very uncommon.”
At times she wishes she could be more like her sister, focused on thriving in the present rather than dwelling in the past.
But there's something about Tracy that she hasn't been able to shake. She says she's searched for her so many times, and so many ways.
When she began searching, she'd misplaced the envelope itself, and feared it was lost forever. She relied on vague details from her memory to start looking.
She remembered the tennis rackets in the overhead bin, so she scoured the rolls of tennis associations. She says she tried contacting American Airlines, too, based on her memory of a logo on the plane. But she didn't have any luck.
The envelope turned up a few years later, giving her more details to look into. Inside, she found a handwritten itinerary she thinks her father had given them before they left home. It specified a different airline and flight number -- KL 655.
She tried reaching out to that airline, KLM, but hit another dead end.
"We have tried to get some info on this case, but unfortunately KLM does not keep any old flight data so it was impossible to find anything internally," KLM spokesperson Ilse Heemskerk said in an email to CNN.
The airline shared the story on its blog a few years ago, and a few people posted ideas in the comments. Several noted it's quite likely American customers on the plane would have been flying KLM on a codeshare flight with Northwest Airlines. "Minneapolis was the NW hub," one commenter noted. "Could have been flying through to anywhere in the Midwest or western U.S."
Zugay says she still wonders whether it was a KLM flight after all.
A recent photo shows Vanja Contino and Ayda Zugay. The sisters say an envelope they received from a stranger with $100 inside is still shaping their lives, decades later.
Courtesy Ayda Zugay
On Reddit, where Zugay has posted about the envelope several times asking for help, she found a supportive community who encouraged her and shared their own theories.
Did she remember anything about what the plane looked like? Did she know if the women played tennis competitively? What about talking to a local news reporter in Minneapolis?
Commenters quickly honed in on the timing and pointed out the French Open would be played around then. Someone suggested she reach out to tennis tour companies.
While many responded to her Reddit posts with ideas of where to look, others were more skeptical. One suggested the chances of success were so slim that her energy would be better spent paying it forward, rather than trying to track down strangers with so few clues.
"The chances are soooooo low and at the same time I don't feel discouraged," Zugay wrote in response. "I want to stay relentless as long as I can. ... They were our first welcome, and they will never be forgotten. I want them to know how the story ends."
Contino, Zugay's sister, is 40 now and an anesthesiologist. She says getting that envelope when they first arrived in the US continues to shape the way she lives her life. She tries to be generous and pay it forward whenever she can.
Zugay didn't speak English when she met Tracy shortly before her 12th birthday. She's 34 now and would love to talk with Tracy in English -- to tell her how she works with nonprofits, cofounded a consulting company and represents Massachusetts as a delegate in the Refugee Congress.
She finds strength in sharing her story.
When Sarah Sheffer heard about Zugay's search, she knew she wanted to do whatever she could to help.
Zugay was speaking on a panel last fall as tens of thousands of Afghans began arriving in the United States after Kabul fell.
Many of the former refugees who shared their stories that day mentioned simple acts of kindness that stuck with them for years, says Sheffer, interim director of the Refugee Advocacy Lab and a vice president of Refugees International.
"Most indelible moments of welcome that the former refugees in the webinar reflected on were really small acts of kindness and generosity -- someone saying 'welcome home' when they got to the airport, or a neighbor who checked in to see if they needed anything," Sheffer says.
“We both just looked at each other, me and my sister, and just hugged each other. Because that's all we had. ... And it was just amazing that somebody was willing to spend that kind of money on us.”
And Zugay's story, Sheffer says, stood out.
"We've got to find Tracy," Sheffer thought.
The powerful story, Sheffer says, is more important now than ever, with the number of displaced refugees in the world reaching an all-time high.
The video hasn't gotten much traction on social media yet since several refugee organizations and advocates shared it this week. And Sheffer says so far no leads have turned up in the organization's inbox. But she knows it's early, and you never know who might stumble upon a tweet.
By sharing the video, Sheffer says the organizations she works with hope not just to find Tracy, "but to show that a small act of welcome really has the power to change the course of someone's life."
But that Tracy didn't recall ever meeting Zugay and her sister, or writing the note, or giving $100 to refugees on a plane. She asked her friend to be sure, and learned they hadn't made the trip from Amsterdam to Minneapolis in 1999.
Zugay still has the text: "My friend Tracy confirmed it was not either of us...good luck with the quest, though."
Ayda Zugay says she's hit many dead ends over the years in her search for Tracy, but she thinks it's still worthwhile to keep trying.
Courtesy Ayda Zuday
Is it still possible that was the right Tracy?
Zugay says she thought so at first, but learning the women hadn't traveled in 1999 after all convinced her that the Tracy she's been searching for is still out there somewhere.
"I don't think we found Tracy. ... I feel like someone would remember something like this," Zugay says.
She's hopeful that the video will get a bigger audience online and may lead her down new paths she hasn't come across before.
"I figured maybe the reach has to be wider to be able to find that Tracy," she says. "And maybe Tracy doesn't hear it, but a friend does, and she remembers the story."
Of course, there are plenty of hurdles that stand in the way.
Some of the details about Tracy may have gotten lost in time or lost in translation.
Zugay knows she might never find Tracy. She realizes Tracy might not want to be found.
Still, Zugay says it's worth it to keep trying.
Maybe Tracy will see this story.
Or maybe Zugay doesn't need to find Tracy for her search to be successful.
Zugay thinks back to one of the Reddit responses she got years ago. It was beautiful, she says -- another diamond in the dark.
"I cannot help you in this search, but can you tell me how I could be a Tracy for someone coming to be my new neighbor/citizen/friend?"
Maybe more people will hear about Tracy and go out of their way to be welcoming, too.
And maybe someday, messages like the one Tracy wrote won't be so rare.
This story is part of "With Thanks," CNN's stories of gratitude from people who've been helped by others in big and small ways. If a recent act of kindness or generosity has changed your life, we'd love to hear from you.