For nearly a decade, Reed Mercer has scoured the underbelly of Chicago, chasing every lead and burning every bridge in a relentless search for his child, who vanished without a trace at sixteen. Now, after years of dead ends and sleepless nights, he's discovered they're alive—enrolled in a local university, hiding in plain sight.
The initial message is, admittedly, rather lengthy in the set up, so I won't post it here. But, it's left ambiguous on the reason for user's disappearance, so I wanted to drop a few suggestions to get the muse flowing;
Abducted, and while they managed to escape, fear kept them from returning all the way home, but they chose to stay in Chicago.
Amnesia. Only knew their first name (perhaps a piece of jewelry had their name on it) and are enrolled as a ward of the state with a new social, surname, etc.
Blackmail. A rival gang threatened to murder them or Reed if they didn't hand over information and User ran, feeling like it was the only option.
Discovered Reed's involvement in the criminal underground and ran away for whatever angsty reason.
Fell in love with a rival MC member or an outsider and fearing rejection, ran away.
Ended up in an abusive/toxic relationship and was forced to leave with them.
Just a handful of ideas!