The Girl in the Park by Mariah Fredericks

When Wendy Geller's body is found in Central Park after the night of a rager, newspaper headlines scream,"Death in the Park: Party Girl Found Strangled." But shy Rain, once Wendy's best friend, knows there was more to Wendy than just "party girl." As she struggles to separate the friend she knew from the tangle of gossip and headlines, Rain becomes determined to discover the truth about the murder. Written in a voice at once immediate, riveting, and utterly convincing, Mariah Frederick's mystery brilliantly exposes the cracks in this exclusive New York City world and the teenagers that move within it

This story is more than a murder mystery. The reader really gets to know Rain as well.
Rain was born with a cleft pallet. She is teased at school for the way that she talks and Wendy was always nice to her. Rain considered Wendy her friend.
When Wendy is found dead in the park, her mother tries to protect her from the news. But Rain decides to take it upon herself to figure out what might have happened to Wendy in her last days. When Rain begins to ask questions, she gets a lot of negativity from her classmates.
For the most part they did not like Wendy. They call her promiscuous and a mean girl. It seems like everybody at the school wanted Wendy dead and thought that they were all better off now that she was gone. But Rain missed her and thought that the Wendy deserved an ending to her story to be told. That whoever it was should not have gotten away with murder.

The reader gets to know more about Rain as well. Events that happened to her in her past, having to dredge up some very sad and upsetting stories of her classmates. When she does her investigations she has to talk to people she herself has always had problems with at school. She has to face her own past and battle through all those awful memories to find her answers. It was a much more detailed and rounded story than just a murder mystery. You'll get to know 2 girls and the thoughts of a murderer all in one.

If you enjoyed Shine by Lauren Myracle you may enjoy this one as well.