"A" IS SEAN!!!

REASONS BEING:

-one day he's cool with Hannah, the next he's not..totally bipolar vibes with this guy.
-there's definitely something more to the 'saving myself for marriage' story. Maybe he just doesn't want to get too close to Hannah because he's secretly sabotaging her and her friends lives as their former "dead" best friend!
-he's jealous of all the times Hannah's ditched him for the group, and possibly was jealous of A from the get go. (This could explain him wanted revenge from all of the girls..)
-he probably had a thing for A
-he is by far THE BEST CANDIDATE FOR KNOWING ALL THE GROUP'S SECRETS

1.)he's friends with all of them!
2.) & HE'S ALWAYS AROUND!
3.)Whenever the girls get texts from where "A" can see them, there's no opposing the fact that SEAN can always see them!

Other possibilities:
The detective?
Spencer?

think of it, If it was spencer, you would see a phone in her hand when she was texting the gurls Its mona. thats why she is never there when the gurls get texts. and, she has bipolar vibes too

HOW DARE YOU!!!
I Mona!
she's is like the 2nd best character in the series!
OHMYGAWD! i just noticed, this is my 100th post!!!!
GASP
i am SOOOOOOOOOOOO x cited!

Im sorry nefaru, its def mona I liked mona too, and then I read the books.

I think that it could or couldn't be mona! since ppl read the books they might change up the show...so it really could be anybody!