All I can tell you is to try and isolate the cats in a room where you know the hamster isn't hiding. And I mean look everywhere twice!! I have had this happen so many times, and every single time, I have found the missing hamster in the room that the cage was in. One thing I have found too is that if I get everything real quiet, and listen...sometimes I have been able to hear them rustling around or nibbling on something. Usually, they have been as far back under the bed as they could get, or behind a bookshelf that was squeezed up next to the wall. Once, when our Rusty got out of his cage, he was in the bed with my daughter!!!

I'm so sorry you're having to spend your day looking, but it sounds like you need to with those cats in the house. Good luck.