The Disappearance of Sabrina Banks

The book is about three young girls that have been friends since grade school. In their junior year of school, they are giving a project for their English class. The project is for them to write pen pals. The pals are trouble children throughout the US. One of their letters gets picked up by a bad man, and he kidnaps and kills the girl. Now the police have to try and figure out who did it and why.