Uuuggghhh, I feel for you. My DS is 14 and has been busted looking at some pretty crude porn sites on our computer. I have had to confront him about it because it has done some damage to our computer.
His dad has bought him some books to read about what to expect during the teenage years, which he read.
I know that my DS is growing up and I have to accept it. I know that he ummm, well you know, pleasures himself - judging by the amount of tissues that he takes to bed with him, and I am cool with that, but I am not cool with porn.
I have explained to him that porn is not realistic, that the majority of girls are not like that and he would be sorely disappointed when a girl doesn't perform like the young ladies do in porn IYGWIM.
Don't get me wrong, I don't mind him having a perv at an attractive girl, bikini clad pinup which I do think is perfectly normal.
Definately have a chat with him about it, good luck..