Teenage years are worse than the terrible two's. You think as our childeren age that things will get easier - but it doesn't. My son is 17. They do change alot during the teenage years and they don't seem to want to communicate much. Everything one does as a parent seems embarassing for them. I know with my son he did put up barriers and want to shut people out.
Without trying to pry into their lives too much - as they need their privacy - it is good to try to find out things that they are 'into'. With my son it is computers and anime. He seems very willing to talk to me about the things he likes - and I make the time to listen to him (and appear interested) and even sit down with him and watch anime with him. It could be a certain type of music he listens to, or what sort of things they are doing at school that he is interested in. Say something that will get him talking to you. It is important to talk with him and reopen that communication. It is a matter of finding what will spark his conversation.
Let him know that you love him - sometimes I will just say to my son, " You are such a fantastic kid. I'm so lucky to have you. I love you so much," and give him a hug - even if he is 17. I do this when we are alone so no-one else can see (so as not to embarass him of course).

Hang in there, everything will work out OK I'm sure.

Lisa