Just heard about this JJ case. Very puzzling & sad. It's especially disturbing that he vanished in the mid-morning in a suburban neighborhood, a time/place most would consider "safe". I haven't had a chance to read much of these threads yet, but here's my take on this: any of these possible scenarios could have occurred, though some are definitely more likely than others:
1) IMHO the most likely explanation is that - since JJ was walking - someone offered him a ride & had nefarious purposes. If he did get into the car, he had a false sense of security - either because he knew the person, or didn't know them but probably didn't get any strange "vibes" from them, etc. I think most of us have it drilled into our heads as kids not to get into a car with a stranger you don't know, but it's not clear how trusting JJ was. That being said - I tend to think that if someone did offer him a ride, it was someone he knew.
2) Someone in a house in the direction he was walking (not necessarily a neighbor, or someone he knew well) distracted him & asked for help, etc. - and got him into their house under false pretenses, etc. However, I don't find this as plausible as #1. For one thing, JJ was on his way to work & I don't necessarily think he would have stopped to go into someone's house. However, this is still obviously possible.
3) JJ had the bad luck to run into a crazy person/drifter while he was cutting through an area without a road/street - and so whatever happened wasn't seen by anyone else. Unlikely.
4) He was hit/killed (accidentally or on purpose) by a car & the person/people in the vehicle moved him immediately into the car - before anyone in the neighborhood/area could see what was going on. Unlikely, especially given the time of day/area & the fact that no trace of an accident was found; i.e., if this had happened, I doubt the people in the car would have stuck around to clean this up, etc. So, I find this the least likely explanation.
I don't believe that JJ was a runaway. Not only was he starting a new job soon, but based on what I've read - he wouldn't have left his family behind without telling them where he was going/what he was doing. Also, a more practical reason was that he didn't have the money/resources to go anywhere & "start a new life".