Try a FT mouse then...it is the smell that will attract him, doesn't matter if he eats it or not. My son lost his king snake once and it showed back up 13 months later!!!! Very skinny but he survived. 3 weeks is way to soon to give up looking, IMO, I would keep trying. Use the cats to your advantage, if they are seeing a snake roaming around at night they should be pretty jumpy. When they are not looking at you make a load noise with your mouth, if your cat jumps, I think your snake is still around. I feed 125 ball pythons weekly, we lose a rat every now and then. When I see my cat sneaking around acting funny I smack my lips real load, if he jumps I start looking for the rat. I have had a couple snakes escape over the years and the reaction from my cat was the same. The longest we ever lost a BP was a few days and the FT rat in a hide worked every time.