I wish they would have had this type of app when I was in High School, to be honest.
I stumbled across this App for iPhone/Android called Calm Harm, and truth be told, it's got to be one of the best apps I've ever seen.
The app, which is from the U.K., has activities that you can use to work through your issues, including Comfort, Distract, Express Yourself, Release, and Breathe.
Each section will also quiz you on what triggered you to have the response you did to the situation, and if you are a self-harmer, will try to distract you from inflicting hurt on yourself.
My favorite part, personally, is the Breathe section, in which a circle pulsates in what pattern you should be breathing for 60 seconds, to help you catch your breath. This particular exercise works best for people with anxiety who cannot slow their breathing.