What you can do is you can close all the doors of your house and in therooms put one of your hamster's favorite food or just some treats. and then come back about an hour or more later and check which room the treats are dissapearing in. Be careful where you step. What i would do is slide my feet instead of stepping because then you wont step on the hamster you would only just bump into him. Don'y vaccum! the hammy will be sucked up.
I wish you the best of luck to find your beloved hamster!