The Gathering by Kelley Armstrong

Strange things are happening in Maya's tiny Vancouver Island town. First, her friend Serena, the captain of the swim team, drowns mysteriously in the middle of a calm lake. Then, one year later, mountain lions are spotted rather frequently around Maya's home—and her reactions to them are somewhat . . . unexpected. Her best friend, Daniel, has also been experiencing unexplainable premonitions about certain people and situations.

It doesn't help that the new bad boy in town, Rafe, has a dangerous secret, and he's interested in one special part of Maya's anatomy—her paw-print birthmark.