The note, which was found by a member of the airline cleanup crew, detailed the unidentified passenger's decision to fly from Miami to Washington, D.C., where she planned to tell a friend she had feelings for him.
"If you're reading this, hello, my name is Andrea," the passenger wrote. "I bought the ticket last night at 4 a.m ... I thought why not, I'll surprise him at the airport during his layover. I'm gonna tell him I have a crush on him."
She added, "I'm going to Australia for a semester abroad in four days and I won't see him for five months so it's really the last chance I have."
Andrea tucked the letter back into the seat pocket, where it was found by the airline worker. A year later, they posted it online.
"Found this in the back pocket of a seat on an aircraft I was cleaning last year," they wrote. "Wherever you are, I hope it went well for you."
Now a search is on for Andrea, who was 21 when she wrote the letter.
People are using the hashtag, #FindAndrea2019, to try to track her down.