The Lost By Natasha Preston

In the small town of Aurora, teens go missing all the time. But when one of Piper and Hazel’s classmates disappears, they become determined to find out the truth of what happened to her. While investigating, they meet three handsome and rich grad students…who kidnap them. The girls are taken to a building in the middle of a privately-owned forest. The building isn’t just designed to keep them locked away—every room is a test in survival. And Piper and Hazel won’t give up without a fight.