You can try some frozen krill, they usually love that stuff. But seriously, he/she might not want to eat. Is there enough water? I think some people get confused about that. We have 6 red ear slider turtles, had them about 3 years (they are huge) and the only time I've ever seen any of them eat is when they are under water. They just pick the food off the top of the water like fish. But if he's tiny, and has been moved from place to place a lot, he might just not feel comfortable/safe enough to eat. I don't know how your set up is, but I would say get a small like 10gal fish tank, fill it half way with water, get a little turtle dock (they are like $6 at petsmart) a fake underwater bush, and a uv light, and he try feeding him again, then wait. Sometimes my turtles go days without eating.
If you have more questions, I can try to answer them for you!