You would be shock at how small a hole they need to escape and just how tiny a place they need to hide. Usually they are found in the same room the escaped in, often less then 5 feet from their cage. It's hard but try not to panic to much. You can try late at night sitting in the room very quietly and listen for him, that is how we found my sister's corn years ago, inside a dog treat box...under the dog treats... Don't forget to check high as well, snakes have been found on top of book shelves and behind hanging picture frames!
How old is the baby ? Another approach it's a lot of work but has to be done. Start in one room top to bottom and look and feel everything my Baby was in the closet I had checked I made a mistake and she was in the boot, I will never make that mistake again, I learned just how clever he was. When I realized he was out First thing I did was close off any holes like pipes and plumming x, this way I know he's inside. I did the flower on the floor never saw a trail . Put some water in his dish and see if he's . thirsty you can flower around the water bowl. He will need water before he needs a mouse I also did night sitting and lost many hours of sleep.