I have two inside cats and occasionally one will simply hide for no reason. Of course they are not "hiding" but simply lying there in plain sight.. if one stands on their head while squinting under the tablecloth through the open cabinet door to the small space under the drawer inside the cabinet itself.
I hope that your baby is inside being naughty. I second the call teh vets, call the shelters and if possible take a picture to all too. Check the shelters personally as much as possible. Some shelters have volunteers answering phones, and are known to say, nope no cat like that here.. without even looking. They are burned out and don't care. Or just tired of hearing, "I have a black cat? Is he there?" Whatever reason, go there personally as much as possible, and asking everyone in the neighborhood. Most cats don't go far, walk the area calling him if you can. You can even shake the food bag as you walk. I've done worse while trying to locate my dog, the one time she got loose. Embarressed? Not a bit. If it recovers the pet it is all good.
GOod luck, and don't panic yet.
Wolfy