Its important to understand the addictive nature of pornography to be sure. Teens are especially vulnerable: http://www.covenanteyes.com/blog/2008/08/27/teens-and-internet-pornography-part-1/

I wish my son would take my advise. He spends hours in his room and refused to use the family computer that we had paid alot of money to block porn and other bad stuff. Then he got a job, of which we were so happy. Only to find out he then spent every penny for a computer and junk that we would never let him have in this house. Now he is 18 and doesnt let us touch his stuff. He is moody and angry most of the time. There is no way you can even talk to him about anything, not even his computer because he calls me stupid and to leave him alone. Helplessly regretting being a mother, I just let him wallow in his pig pen.