Did you just buy him/how long has he had to ajdust to a new home? How old is your gecko? What is the setup like; temps on both sides, substrate, how many hides, etc?? Is he eating anything at all? Does he ever poop?
Try pinkies, my gcko loves them. I feed them to him every 3rd day and he gets ftter and fatter. I read in a book to feed pinkies to them ever 3rd day so just give it a shot. If that doesn't work you should try fixing up the cage to look more appealing and more homely. My gecko is picky at what was in his cage and so is my female.
Adam, you need to raise the temperature to 90-92 on the warm end. Are you using an undertank heater? Leos need belly heat to digest their food, so if you have not got one, I suggest you get one soon.
I agree, the temps. are most likely your problem. If you're using a light bulb for your heat source, just get a bulb that has about 20 more watts than what you already have.