My Mom, who was given the task of cat-sitting for a week, is worried sick. My soon to be Sister-In-Law has had this cat for over ten years.
THIS IS NOT A JOKE.
I agree with letting the house get peaceful and quiet and at the same time leaving a bowl of wet cat food or tuna out but in a semi-hidden place so the cat doesn't need to step into a wide open space to get to it.
The cat may be so afraid and sad that it's not eating and drinking enough to use the litter box.
I think better would have been for you or a reputable pet-sitting company to have visited the cat at home and fed it while the owners were gone. Cats HATE to change environments. It is very stressful for them.
But good luck!
By any chance is the sofa a hide-a-bed? That's where my reclusive kitty hid when I brought her home as a 2-y.o. I literally had to open the thing up after looking everywhere else. She'd squeezed herself into the works, inside the couch. Also check the backs of any upholstered furniture where there's often no stuffing to block kitty's climbing in from underneath.
Good luck!
Congrats on finding the cat.
Sorry I am so late on this thread. I once lost a cat and an entire litter of kittens. Looked everywhere and finally heard kitten sounds under the couch. Still couldn't see them. They were in between the fabric liner and the bottom of the couch!
Cats are endlessly entertaining. Glad you found the scoundrel!