What can I do about a teenager bed wetting?

Hypnosis. Teens often respond beautifully to hypnosis. See a physician skilled in this therapeutic modality.
See his doctor. Has he wet the bed his entire life or is this a return of wetting after having had a pattern of dry nights? Either problem is best addressed by his doctor. While awaiting his doctor visit, make sure that he is not constipated as this can exacerbate the problem. Don't blame, punish or redicule for wet nights. Praise him for dry ones. Consider a bedwetting alarm as this can train most to stay dry.