Try to find your hamster during the night because the chances to see it awakened are higher. Be sure he/she can't get out of the house and that there aren't other animals that can hurt your hamster that escaped. If you hear any strange noises in a room, close it and search your hamster there. Put some hamster food (specially fruits or food you know he/she loves), water and a nest in a box, in a way the hamster can enter it, but can't leave it. So maybe during the night he/she will enter it and sleep there. In the morning you'll be able to find it there.