Your answer can be found in the official Catechism of the Catholic Church:
2352 By masturbation is to be understood the deliberate stimulation of the genital organs in order to derive sexual pleasure. "Both the Magisterium of the Church, in the course of a constant tradition, and the moral sense of the faithful have been in no doubt and have firmly maintained that masturbation is an intrinsically and gravely disordered action."137 “The deliberate use of the sexual faculty, for whatever reason, outside of marriage is essentially contrary to its purpose.” For here sexual pleasure is sought outside of “the sexual relationship which is demanded by the moral order and in which the total meaning of mutual self-giving and human procreation in the context of true love is achieved.” 138
[137/138 footnotes: CDF, Persona humana 9.]
The fact is, according to the Church, masturbation IS a sin. Some teens (and even grown men) have had problems with this sin, but please realize that it can be confessed. Ask God to give you strength in coping with this. You might also want to ask Saint Dominic Savio for his intercession to help you. He is the saint of teenagers. To find out more about him, you may go to this website and read about the guy -
Also, Amazon.com offers a list of books about him.