My oldest son is 15 and to be honest, I would be in the same boat you are.  I wouldn't know what to do.  If I were to place myself in your shoes I think I would have an intervention.  I come from a large family so I believe I would have everyone there waiting on him one day to talk to him.  No one that would place blame but people who deeply care for him.  Now that may be something that would only work in a perfect world, but it might be worth a try.  This way you wont have to confront him alone and he may just realize how important he is.  Although I do have to say that if you are truly afraid of him maybe your best bet would be to have him arrested on his warrant and beg the court for rehabilitation.  The warrant issue has to be cleared in any event.  I wish you the best.