Start in the room they are in on one side, check HIGH and LOW and in between, looking in dark spots, and warm spots (Near electronics/behind your cable box/computer/tv/anything that heats up when on is a good place to start). Once you have gone from one side to the other of that room branch out from there doing the same to each room then moving on. That way if he is still inside your house you will find him.
Main thing is to be sure to not hurt/crush him when moving stuff looking for him or that your dogs get ahold of him.
GOOD LUCK and keep us posted if you can!
Would he try and get into a heating vent? That's the only place I can't look.. otherwise my house is a ranch, there's only so many places for me to look.. still can't believe this happened.