Help me find a book!

[Seeka 12,372]

So... My writing bestie is looking for a book. He doesn't know the title or author, but he remembers the premise. 

It's about a mall where teenage suicide victims are sent to become ghosts. The main character is one of these new ghosts. 

Any of you guys know this book? My bestie is writing something similar and he wants to know how they did it.