Another way to approach the situation is to go to the bookstore with your sons and purchase popular culture magazines for young men. Many of the magazines portray alluring images of women. These images may not be as explicit as the material that you found, but they can definitely be used to get your point across. Emotional Health is one selection to consider. It's pretty common for parents to find sexually explicit material in their teenagers' room.
Adolescence is the time of sexual discovery.
Many men are visual, and looking at porn is a way to learn about women's and men's bodies, as well as about what arouses them. When teens masturbate while or after reading porn, they're often focused mainly on release and pleasure. Solo-sex, with external stimuli or not, is also a form of safer sex. Continuing to have open and honest discussions with your boys about sexuality will help lay the foundation for your teenagers to mature into sexually healthy adults.