It certainly won't help to embarrass him, and cry and storm about pornography. That doesn't mean avoiding the important questions. For some boys a nudie magazine is an opportunity to satisfy curiosity about the anatomy of the opposite sex. For others there is pleasure in the beauty of the female body. God designed a woman's body to be very attractive.
Many men have a fascination with women's breasts.
But appreciation of beauty is very different from using hard core pornography to think about raping a woman. If your son sees you are horrified at any mention of sexual feelings, he will clam up. He will make sure a large area of his life is never open to you again. This is why many mothers lose communication with their son in their teens. Harsh judgments, cruel condemnation, and humiliating embarrassment are always fatal.