Most teenagers display a lot of "normal" transitioning behavior. Some call it "the process of individuation." The main issue with being a mother of a teenager is to realize that we have moved from a manager's role to a consultant's role. The greatest influence we have is helping our teens trust us, and our judgments, and encouraging them to come to us for advice.
Many parents have found that making time to do things together regularly creates an environment for communication. It's also important to not take things personally. If, during this period of individuation, your children need space, it's fine. If they are angry, down, or any other place in between, it's probably not because of anything you have or have not done and is rather due to their emotional development.
Reminding your teenager that you are there for him if and when he would like to chat with you is sometimes all he needs to hear. He may open up to you immediately, or it may take some time. Remember that when he does come to you, he does so with the hopes that you will be open to hearing what he has to say, that you will reserve your immediate judgments, and that you will simply be a safe person to discuss whatever's on his mind. You have worked hard to raise him with that idea in mind, and he looks to you to continue to maintain that level of empathy and compassion.
There are some wonderful books for parents of teens. One we particularly like is Uncommon Sense for Parents with Teenagers by Michael Riera.