Comedown (2012)

Six friends who have known one another from childhood break into the tower block they lived in as kids, now deserted and condemned, to rig up a pirate radio station, get high, and party. When one of the group goes missing, her friends search the dark interior of the tower and soon realize that they are not alone: a resident psychopath lurks in the shadows and is hunting them down, taking them out one by one.