As this article notes, 15-year-old Wendy Eaton disappeared from Media, Pennsylvania on May 17, 1975, 46 years ago today. She was walking away from her home, towards the downtown area, when she vanished. Dogs tracked her scent to an intersection, then lost the trail, suggesting a car picked her up.
There doesn’t seem to be much in the way of evidence as to what happened to her (though the article does provide a clothing description I hadn’t had previously). If she’s still alive, Wendy would be 61 today, turning 62 on the 26th. Sadly I think she’s still fifteen.