What causes lead to teenage suicide?

Suicide is a tremendously complicated subject.

Suicide in teenagers more so.

Those who successfully attempt suicide generally tend to be males in their twenties with a history of serious mental illness (usually, but not always, type 1 Bipolar Affective Disorder), a history of alcohol and drug abuse, a history of suicide in their families and access to deadly weapons.

As you can see, the general trend is that teenagers are unlikely to successfully attempt suicide.

The trend is complicated by the fact that unsuccessful attempts are most likely to be made by females in their teens. Which puts us right in the wheel house of your question.

Female in their teens who attempt suicide have a particular set of increased risk factors.

Suicide attempts are obviously co-morbid with mental health disorders (only the terminally ill, in most Western countries, choose to commit suicide for reasons not based on mental health). This group is generally too young to be Bipolar (the leading mental health risk group for suicide), as that disease typically has an on-set after age 19. Thus depression and personality disorders would be greater causes in this age group. In this group there is also a strong co-morbidity with eating disorders, particularly anorexia nervosa; eating disorders are overwhelming co-morbid with a history of sexual abuse.

So the leading causes for attempted suicide in one's teens (and the attendant risk of a successful suicide) include; the patient is female; the patient is depressed or suffers from a personality disorder; the patient is anorexic; and the patient has a history of sexual abuse.