Try putting a small new frag in the front of your tank where you can net it easily, shrimp are inquisitive just sit and wait when he goes to investigate net him
Take a clean empty pop bottle and put some sinking pellets in it, soak them in garlic and selcon to make them smell yummy and put it in at night, come back about 15 minutes later and he'll probably be in there, plus a bunch of pods and bristleworms.
Do what the other guy said about the plastic 1 litter bottle except cut the top 3 inches off the bottle and flip it around and stuff the top back in the bottle. When the shrimp goes into the bottle to get the pellets it will get trapped. Ive pulled out three peppermints today. If you just put in a regular bottle the shrimp will shoot out of it too fast.