2 choices i can think of......hollow wall anchors(molly bolts) or find the studs the drywall is screwed into(has to be some or it would sag/buckle in the middle or seams). stud finder or magnet will work. magnet has to be a good one not like a fridge magnet. drywall is heavy it has to have something underneath to hold it up. depending on the age of your home and building codes the studs should be every 16" on center. if its older try 18" if its an attic space the joists will be between 18 -24" on center depending on trashed the framing crew was...not kiddin im a contractor and see it everyday. id need more info if that doesnt work.