If he has any connection to his parents at all, the embarrassment of being outed in front of his parents might be more than just a slap on the wrist.
Also, is this the "an eye for an eye" theory of justice? Personally I hope that my kid will behave in a good way because he considers it the right thing to do, not because he is afraid of punishment.
It's not an eye for an eye. But it is actions and consequences.
If you take an extreme crime (like murder), I don't think you'll find many people who would say "there should be no consequences to that as long as the person is truly sorry for what they did". There must be some level of punishment, and there will be disagreement about what the appropriate level is.
Now this was not murder, but it was true terror over a period of 4 years. Do those actions have consequences? Or just give him a hug?
This 17 year old has problem, and he needs intensive psychological counselling at the very least. He didn't know why he did it? It was just a game? Those are scary answers and the problem needs to be fixed.
At least having him in the police database, fingerprints, IP address records, reports from his counselling sessions - would make it easier for someone else to catch him next time he does this. The next person he does this to will be starting from scratch trying to find out who this was, like the author was 4 years ago.
Also, is this the "an eye for an eye" theory of justice? Personally I hope that my kid will behave in a good way because he considers it the right thing to do, not because he is afraid of punishment.