This is my theory, too. I think the most obvious answers are likely the right ones. That he was a teenager likely in and out of trouble before he left home. The family didn't look for him because they probably had already given up on his lifestyle. I knew someone in AA who had a story like that. Perhaps that star tattoo was a youth sobriety thing, and maybe he fell off the wagon and got on tour with the Dead.
I think a lot of the clues that were dead ends do fit together... The guy who says he picked up a kid with two carolines and couldn't find them again so left RFK stadium with their stuff... the new photos that surfaced suggesting he was from SC... his ID and belongings were in that guy's car, but they never met up again... so he had to catch a ride south where family lived.. because what else would you do if you were in your late teens and suddenly lost everything after months or years of feeling free and invincible... head home to SC to family to hopefully take you back in again... or to clean up his act in the process of getting a roof over his head this time... maybe he really was in Illinois because that's where he was when the money ran out the prior year. The Dead played in Chicago in July 1994. Money ran out so he set up and got a job at McDs to get enough money through the winter and head back East in 95 once the tour started again.
This kind-of reminds me of
Alexander Supertramp. Just a drifter who wanted to be free from parents & teachers, but a drifter that had his luck run out. (It also reminds me a little of the attitude of Band Aids in Almost Famous) He thought he'd catch a break by "floor surfing" and catching rides in the Summer East Coast tour '95... maybe with the intention of getting closer to home... and ultimately he lost in the end... Poor planning, too much dreaming... Family tried to help him before he left, but he was set in his ways and they didn't know to report him as a missing person (sometimes you can't help someone who won't help themselves)... Chalked him up as a runaway....
I do really think he met the driver prior to the day they died, though. I don't really know how, but I feel it. They are too similar for it to be a hitch hiking situation. Both deadheads, both going from DC south (and as we think, possibly to SC).
I wish there were more leads on the Carolines. That would really help.