Answer:
Here are some ideas. First, you have to be really quiet. Wait until you hear noises, like shuffling, scratching, squeaking or the such. Take a small flashlight or something and look around places like sofas, couches, chairs, and little corners. After that, (if you still can't find your hamster) get your hamster's absolute favorite food. Leave it there and hide in a close place and just wait. Put multiple spots of food for better luck. The last resort is to buy a non poisonous rat trap. The one I used to catch my hamster is just a trap that closes in the back when something goes through the door. It will hurt your hamster if it's fat, so this tip is mostly for dwarf hamsters or small-ish Syrians and teddy bears. Leave it there, and dab some peanut butter on the trap. Then wait. Soon, you'll hear struggling in the trap, so go look. Put these traps in small corners, or behind big furniture. Good luck finding your hamster!
-E