Goodreads - Set reading goals, keep track of what you read and get book suggestions from friends  

Teen Book Finder - Book suggestions from YALSA (The Young Adult Library Services Association).  

Penguin Teen - Great source to find upcoming titles, best sellers and discover new favorites from Penguin Young Readers

Fantastic Fiction - Source for all things Fiction.  You can follow your favorite author and learn about their works.  There are reviews and book previews to see if you might be interested in reading it.