Pretty Little Liars (2010)

Set in the fictional town of Rosewood, Pennsylvania, the series follows the lives of Aria Montgomery, Hanna Marin, Spencer Hastings and Emily Fields, four girls whose clique falls apart after the disappearance of their queen bee, Alison DiLaurentis. One year later they begin receiving messages from a mysterious figure using the name "A" who threatens to expose their secrets. At first they think it's Alison herself, but after she is found dead, the girls realize that someone else knows their secrets—including long-hidden ones they thought only Alison knew. Alison was also stalked by A, and the girls continue to find more and more information about A and Alison's disappearance - all while risking their lives.