If you follow teen book trends at all you have to have noticed the recent blow-up of paranormal romance out there, especially since the advent of Twilight. Why, you may ask. Kiersten White, author of NY Times best selling
Paranormalcy and
Supernaturally offers her opinion:: all you need is love (in the timeless words of the Beatles.)
Ms. White believes that paranormal romance is the ultimate metaphor for teen romance. Everyone who has ever yearned for someone with rosy cheeked bloom of young love understands how the object of your desire can often seem alien and a from a completely different world than you. Most teen love is that of idolization, you don't deserve the affection of your desired "other", let alone possess the ability to get them to even notice you.
Paranormal romance takes the inherent struggles of young love and blows them up into crazy/dramatic proportions. Whether it's the broody guy you sit behind in Calculus who seems "oh so mysterious," or a vampire who has to restrain himself from sucking your blood, you know the struggles of the young heart.
I can understand that, most everyone can understand that (unless you somehow were lucky enough to skip those painfully awkward teenage years and skipped straight to Cassanova status.) And who doesn't like to read a good book or two that they can relate to?
Paranormal romance just happens to be particularly relate-able to our
lovelorn younger selves.
Sources
http://kierstenwrites.blogspot.com/2010/07/you-cant-kill-undead-or-paranormal.html
Series have always been a handy way to get reluctant readers to become invested in a story and WANT to read. Book series have become more and more popular in adult fiction as well in the last decade. I think that perhaps the correlation lies in the increased popularity of reading for fun, especially with our teens and tweens. If more people are reading, we need more books for them to read. 
