First, figure out why your teenager isn't listening. It may be painful, but think about what kind of example of communication your teen received as a child. If you responded to your children disrespectfully or with put-downs, it could be that now is payback time. It's not too late to apologize and tell your teen that from now on, you're committing to mutually respectful communication techniques, and you give him or her permission to point out if you say anything that's offensive.
On the other hand, it could be that you were a wonderful parent to your children and now they're going through typical teenage moodiness and trying to figure out identity issues (just because my parents are religious doesn't mean that I have to be) or to experiment with other lifestyles (the neighbor's teenager hangs out all night; that looks cool. I don't want a 9-to-5 office job; I want to join the U.S. Navy SEALS. What does using cocaine feel like, anyway?). If your teen doesn't want to listen to you, decide whether a particular issue is worth taking a stand on, or if it's something you can live with. If you ask a parent support group if your expectations are reasonable or if you're over-controlling, you'll get a third-party appraisal of the situation.
Write a short note about your concerns (add a compliment or a loving message and your teen might hold on to the note for years) and hand it to your teenager; ask a relative or friend with whom your teenager is on good terms to talk to him or her; or build up your relationship by going out for pizza or ice cream once a week and then try to communicate again. Try to stay calm and patient, and let your teenager know that whenever he or she is interested in talking, you'll be there to listen.