Wish You Were Dead by Todd Strasser
An anonymous blogger named Str-S-d announces that she hates Lucy Cunningham and wishes her dead. A few days later Lucy disappears. Madison Archer drove Lucy home the night she went missing. Madsion receives messages that warn she could be next. The mysterious blogger posts another name and that student goes missing...and then a third. Madison decides that she needs to find her missing friends before it is too late. In addition to the strange blog postings, Madsion receives hastily scribbled notes from a "friend." These notes provide clues as to the circumstances surrounding the disappearances of Madison's friends.
Madison is so freaked out by all of this that she hardly notices the attentions of Tyler. He is the new boy in town and kind of mysterious. No one knows much about him. He and Madison work together to find their missing classmates. As Madison and Tyler become closer, there are some details that are revealed about him. He is not who he says he is and has a motive for being in that town that goes beyond going to the high school.
Another great book from teen favorite author Todd Strasser. This one will keep you on the edge of your seat, and you won't believe the ending!!