First of all, I don't think that there is all that much danger of censorship in the US today. However, we will go with the idea that it is a danger and teens need to do something about it.
Most censorship in the US today happens in schools or public libraries. Typically what happens is that parents complain that some book or other is not appropriate for their children to have to read. This is often because the book has too much sexual content or because it tallks about things offensive to someone's religion.
So I would say that the best thing that teens can do is emphasize to their parents that they are old enough to handle reading things that have these themes. They should tell their parents (if this comes up) that they can read things and make up their own minds and that they do not need to be protected from this kind of stuff.