What is the best treatment for teens who self-harm by cutting?

No simple answer: There should be a good psychiatric evaluation, then an appropriate treatment plan be developed.

Cutting: Teens are at higher risk for drug use and cutting, as well as other risky behaviors. This kind of acting out is done as a way of communicating what are often very complex feelings about themselves, their world, their future, and in my opinion, DEEPLY conflicted relationships with people in positions of authority.

DBT: Dialectical Behavioral Therapy is the gold standard for treating patients who self -mutilate.