This article looks at why trying to use shame to get your teen to avoid sex is unproductive and potentially damaging
http://genderacrossborders.com/2010/07/29/shaming-teenagers-about-sex-is-a-bad-idea/
And this article offers advice on how to talk to your teen about sex:
http://www.modernmom.com/article-7998-how-to-talk-to-your-teenager-about-sex/
And some research on which parents talk to teens about sex: