P.M.
Kids in their teens quite naturally want to begin the process of emotionally separating from their parents. They want privacy and independence. If your child tells lies that keep his/her life more private, that may be quite normal. It's not necessarily healthy, though.
I would suggest you read How to Talk So Kids Will Listen, and Listen So Kids Will Talk. You can read part of this really practical guide to communicating with your kids here: http://www.amazon.com/How-Talk-Kids-Will-Listen/dp/038081.... I think you'll be impressed with the possibilities.