I thought I lost my trigger on the weekend. I checked my overflows 10 times and each time I fully convinced myself "there are no fish in here." Guess where he was? They are the darndest good hiders/camoflagers sometimes. Also second the suggestion to check your pipes and so on. You never know.
Good luck, I hope you find him.
It's not impossible about the cat theory, but fwiw, I kind of doubt it too. There'd be some evidence, they're not exactly the cleanest/neatest of eaters when they're eating a whole animal.
