A Line in the Dark

If you're looking for a book where the main character is basically a creepy stalker, but that's not at all addressed in the story then this book is for you.

Jess is annoying and obsessed with her best friend/crush. Angie is the vapid pretty girl. Margot is Mean Girl #1 and Ryan is Mean Girl #2 (because they always come in pairs). Emily is in this story for some reason, but we never find out why (actually now I'm questioning if her name was Emily).

A billion pages into the book something happens and by the end of it you're pretty sure everyone is a sociopath. The End.