Nascar Nurse!!! I have been where you are! My perfect son turned 15 and suddenly turned into a person I never expected. He was a top student, helpful at home, perfect child, people commented on his appearance and his manners..............and then it happened.
I went through about 2 years of hell with him. He snuck out of the house, went on drinking binges, met up with some very odd characters, stole his father's car and drove to New York City with some other kids, all kinds of things I would never have imagined he would do.
He refused to go to see a councelor, so I took him to court and put a "child in need of services" certificate, which basically was a judge telling him he had to go to counseling. So off we went to see the counselor. bottom line was the counselor told me that my son knew right from wrong, and he was doing much of this just to make me angry!
To make a long story short - he ditched the horror show friends, ditched the horrid girlfriend, and got back on track. He is now married, a proud father of one, and works as a teacher in a community college (and spent most of his teen years hating school).
A few years later - on public television - there was a documentary about what happens to the brains of teenage boys when the testosterone starts to peak, at about age 15, 16 17 or thereabouts. I was shocked to hear the story of my son on this program. I wish I knew the name of the program, so I could get a copy of it, as time after time I hear the same issues from other mothers. The story explained that something happens to cause a chemical imbalance in the brain, much like what happens in huntington's disease, where the impulse control switch is turned off. And that's a pretty good explaination for why a model child suddenly flips like that.
I wish you well with your son. All I can say is, it is very very difficult to live through this, but in the end, the values you taught him will shine through. He will survive this, and so will you. He will once again return to the child you know and love, it will just take a while. Keep strong, continue to point him in the right direction, because even if he does not listen, he still hears.
All the best to you.