It Follows (2014)

When carefree teenager Jay sleeps with her older boyfriend for the first time, she learns that she is the latest recipient of a fatal curse that is passed from victim to victim via sexual intercourse. Death, Jay learns, will creep inexorably toward her as either a friend or a stranger. Jay's friends don't believe her seemingly paranoid ravings, until they too begin to see the phantom assassins and band together to help her defend herself.