As you probably know, hamsters are not truly nocturnal. They have 2 main time periods where they have a burst of activity - around sunrise and sunset where they would gather food for the day, so those times of day are excellent times to look for your hamster. Look for him running along hallways or along walls.
When I was a teenager we had 2 major break-outs:
1st - 1 escapee - lost for a few days. I had a dream she was in the downstairs coat closet in a shoe and weirdly enough - that's where she was! She'd also managed to aquire a stash of goodies in that shoe.
2nd - mother and her entire litter of half-grown baby hamsters escaped
(my parents were very displeased). Somehow my father heard scratching in the wall. He isolated the sound and removed the medicine cabinet in the downstairs powder room and the mother and all her younguns tumbled out. They got into the wall because my father had removed the plumbing access panel on the upstairs bathroom and they all went exploring. Not surprisingly, that was the end of hamster-keeping in my parents house.
A few years ago, my son had a hamster escape for a few hours, but we found her. She was running along the wall in the den at sunset.
I agree with Silkie chicken about glass cages with locking tops. Hamsters are good climbers!