try and lure your hamster back into an area you can get him with a trail of sunflower seeds. when you see him/her you cant freak out or it will scurry away.
Ok, that's one(amature) way to do it. here's a better way.
-make a trap. get a tall, metal bucket put a small dish rag in the bottom and place a peanut buttered cracker. make a stair way out of books leading up to the bucket and make sure your little guy/lady will not be able to get out.