Wow, I am really sorry to hear that his identity until now was learning torah and wearing black and white clothing and now that he has shed this “identity” he has nothing else to fall back on, no developed skills, no developed talents, nothing. I guess he feels empty and has absolutely no reason to get out of bed these days. I dont blame him…That is a sad, sad situation to be in:( Perhaps you can send him to a kibbutz where he can learn to work the fields or perhaps learn how to fish or something similar to that. of course, I am assuming your answer will be that you want him to be religious and so going to a kibbutz is out of the question but I think for now you need to overlook religion (or find a religious kibbutz)and focus on his mental health. give him a real reason to wake up in the morning and working on a farm will def give him a good reason to do so. plus, it will keep him safe and away from the street people you seem to despise.
regardless of whether you take my advice or not, i think that your other children are in danger as well (even if it seems that they are doing ok right now, they may be faking it and waiting to see what happens with their older brother before becoming rebellious themselves). are they also too busy learning torah to take classes that will help them develop their skills and talents that Hashem gave them? what will you do if one of them starts acting out in the future? the least you could do, is give them a chance now, put them in karate classes or on sports teams or let them learn how to play an instrument etc. so they develop their self-esteem now instead of falling through the holes later.