They're Watching You - Chelsea Ichaso

When a secret society has you in their sights, it can lead to power, privilege... or death.
It's been two weeks since Polly St. James went missing. The police, the headmistress of Torrey-Wells Academy, and even her parents have ruled her a runaway. But not Maren, her best friend and roommate. She knows Polly had a secret that she was about to share with Maren before she disappeared— something to do with the elite, ultra-rich crowd at Torrey-Wells.
Then Maren finds an envelope hidden among Polly's things: an invitation to the Gamemaster's Society. Do not tell anyone, it says. Maren is certain her classmates in the Society know the truth about what happened to Polly, though it's no easy feat to join. Once Maren's made it through the treacherous initiation, she discovers a world she never knew existed within her school, where Society members compete in high-stakes games for unheard-of rewards—Ivy League connections, privileges, favors.
But...