I've done a lot this past week as my second YA book was released including joining here

Facebook fan page
Twitter
I have a blog.
I joined:
Goodreads
LibraryThing
Authorsden
Kindleboards
Nookboards
Shelfari
Absolutewrite
bookandreader
I join forums and talk to people, promote where I can. It also helps when you're writing for YA to have a teenager

My oldest has spread the word to her friends. Hopefully, some of these things will help.