Perdita5

"My perfect life was a lie. Now I'd do anything to uncover the truth.... Not long ago, I had everything a girl could wish for: amazing friends, an adorable boyfriend, a loving family. But none of them know that I’m gone—that I’m dead. To solve my murder, my long-lost twin sister, Emma, has taken my place. She sleeps in my room, wears my clothes, and calls my parents Mom and Dad. And my killer is watching her every move."

Shortly before her 17th birthday, Emma discovers she has a long-lost twin named Sutton Mercer. She contacts Sutton, who agrees to a rendezvous but never shows up. Curious at first, Emma slips into Sutton's ultra-glamorous life, assuming her identity. When it becomes clear that Sutton is not coming back, that someone made sure she never could, Emma plunges in to investigate who could have wanted her sister gone (a fairly long list, she discovers).