So far I have only read the first book in the series. I grabbed it for my daughter at a second hand store and mostly wanted to see how close it was to the tv series.

Book 1 is pretty close. As far as books made into tv series go.

I enjoyed it, it was a very quick read and definitely something a preteen could read.

The Pretty Little Liars book series (16 books) by Sara Shepard is a thrill. The books start out quite similar to the TV show, but quickly deviate, as it would not make sense to have the TV series follow the books exactly, as readers would already know the end outcome.
The books have so many twists and turns and new characters, but they suck you in and keep you coming back because you just have to find out what happens.
Definitely a good young adult series.