This is a very difficult struggle that may take a long time and a lot of effort to overcome. The biggest advice I can give you is to go to Confession regularly. I realize as a teen this may be difficult, but give it your best shot.
There is tremendous grace and power to free you from this addiction in Confession. Again I'm not promising it will be immediate but you will get some traction.
Know yourself and your triggers; avoid what are called occasions of sin. These are not sins in themselves, but situations you find yourself in that tend to lead to sin.
For example, if you find you masturbate when you're bored, keep busy.
You know your triggers; neutralize them. We have a lot of answers on this topic; check out the following: