What would happen if a teenager shows up without ID, not knowing everyone and couldn't get home?

This is an entirely fictional scenario, which sometimes go through my mind. What if one day a kid or a teenager turned up without identification (or worse, invalid identification), and despite what he claimed, couldn’t find his name registered in his high school, all the numbers on his mobile does not work or connect to the wrong people, and his home is inhabited by total strangers?

Detain him as an illegal migrant? Send him to a hospital ward?

Personally, I’d wait for Ah-nuld (or, since it’s 2009, The Rock) to show up and help him get back to his home planet. Because what you’re describing is basically a science fiction story.

Something pretty similar was reported last week in the national news. I suppose someone will claim her eventually but she is stuck in that situation now even though it is possible she is faking it.

What do you mean by “turned up”? There are plenty of homeless teenagers out there, most of whom probably have no valid ID and all of whom by definition have no permanent residence. I wouldn’t expect this kid to be treated any differently than any other homeless teen.

Or are we to assume that he went to the authorities asking for help in finding his family? In that case I doubt he’d be treated as an illegal alien unless there were some additional reason to suspect he was a foreign national. If he had a heavy foreign accent or his personal belongings were foreign brands not readily available domestically then his immigration status might come into question.

If the boy were making claims about where he lived or went to school that weren’t supported by official records then he might be sent for a psych evaluation. Maybe he’s delusional, maybe he has amnesia, maybe he’s a runaway trying to avoid being sent home. If he were deemed to be a threat to himself or others he’d probably be committed, but otherwise I’d expect he’d be placed in foster care. The local authorities would no doubt contact the media asking for help in identifying the boy and finding his family.

Foster care

Clearly Biff stole his time machine and Sports Almanac to give to himself in the past, thereby creating an alternate future under his corrupted reign.