If you or someone you know has lost their cat,
see Recovery Tips - Lost Cat Behavior
The Silence Factor
is important to know about. Veterinarians are usually familiar with it.
After searching our house, I found one of our cats hiding under an ottoman/ footstool thingy with a skirt. She was not feeling well, so she hid. I took her to the vet & found out she had kidney disease.
"The Silence Factor kills many cats
because while the cat is sick or injured and hiding under a neighbor's deck, cat owners are typically busy "looking" for their cat down at the local shelter or they are busy posting flyers on telephone poles. Instead, the proper search for most cats in most situations is to conduct an aggressive, physical search of the immediate area while understanding that the cat might be close by but hiding in silence."
Much more behaviour-based & search advice on that site.