Main culprits- Drugs and Groups.
Shame, embarrassment ,fear come into play and since they aren't trained to cope with pressures and demands associated with the above, suicidal tendencies creep in.

Doesn't matter how well brought up a kid is.

Among teens the biggest culprit by far is "bullying", and fits very much into the "abuse" context, even cyber bullying, even when it is unknown to the parents and so on, e.g kids (boys) my want to hide their 'weaknesses', teens are very self aware and when you mix them with some overfed kumbaff boys from terrible backgrounds where the mother/workers is/are regularly pounded and bullied by the father e.t.c this kids form a gang in schools and export the behavior from their terrible parents and bully "weak" targets to a point of suicide.