A UVB bulb might help stimulate his appetite. Here's one: Zilla Tropical 25 UVB Fluorescent 13 Watt Coil Bulb at PETCO
Though the ones I usually see are 5 or 10 UVB. I've heard about frogs starting to eat after getting a UVB light, though everyone doesn't think they NEED one. I don't use one because my frog is albino but I may get one if I get another frog.