I don’t believe that many of the kids who go off even know why they are off and how they ended up there. Usually the kid has to come back on to a certain degree before he gains the self awareness and honesty to really understand what happened and how he got there.
What I mean is usually the kid is unhappy he will then start making lifestyle changes and meet bad friends and one thing leads to the next. If you asked him why you are off the derech he wouldn’t say “because I met bad friends who introduced me to drugs and who knows what…” In most cases the kids will say that it was my Rebbe or parents or whatever. The Rebbe may have been what made him upset but without the Internet or without the bad friends he would never be off the derech. So with Internet what happens is that the person is usually unhappy with their life for whatever reason and become curious and start “looking for things” either out of boredom, unhappiness, or pain or whatever. Then unfortunately they learn about negative things online and they change their lifestyle and start going to the places they learned about online…