I have a nephew who became very ill with schizophrenia. The symptoms started off like those of your son. But soon he was hearing voices and everything really degenerated. If I were you, I'd take him to a psychiatrist for an assessment.

Schizophrenia has more symptoms than withdrawal - sometimes paranoia, sometimes psychotic episodes, sometimes not being able to keep clean or look normal. This boy is just withdrawing - maybe he's depressed. Also, sometimes teenagers just go into intense moods. But I would still take him to a counselor to try to help him.

I think when your kid has a personality change something serious is going on. Maybe he is being bullied or maybe he's been abused. It's really important to get him professional help. Maybe he's on some weird drugs. So many things could be going on. My brother became "weird" when he was a teenager and it turned out that he had depression. Once he was diagnosed and treated he was his old self again. I was very affected by his illness and I read a lot of books about this stuff. Parents have to help their kids because the kids can't always help themselves.

This means that your son is reaching out for help, and everyone around him has appeared to give up on him(from his point of view).  His behavior suggestst that he is hiding something, and does not know how to ask for help.  The mere fact that you got a "maybe" from him shrugging his shoulders is a great sign that he wants help.  PLEASE help him before it is too late....