If he's pretty small, the poops might be camouflaged in the substrate if you're using loose substrate. But if you're using paper towels, and still not seeing anything I'd say 2 weeks is pushing it. People on other forums say as long as you see poops then your gecko is eating. If you're not seeing poops I'd be worried after two weeks. But, geckos typically don't starve themselves so it might just be adjusting still.