Question - do you know all of your neighbors? I only ask because earlier this week when OUR cat was missing and we finally heard him outside, when we called to him, he came running to us from a neighbor's patio. We are fairly certain that he was coerced inside their apartment by food. Those neighbors had been eyeing our Mishu ever since he was in the neighborhood and that was partly why I was keeping him indoors. He is a beautiful, long, lean regal-looking all black cat (he's got a bit of siamese in him, so you can imagine what a pretty-boy he is) and he's EXTREMELY sociable with humans. He knows (and responds to) his name and as I'm certain our neighbors have heard us call out to him before we decided to make him indoors only, they too know his name. I'm not saying that they did so with malice, but he is a hard cat to resist. I would most definitely go to all of your neighbors and stress that he is not only very loved, but very missed by his mommy and daddy.
I was frantic when we couldn't find Mishu and only too relieved when we got him back. Such terrible thoughts ran through my head and hubby tried in vain to reassure me. Stay positive. Cats have great survival instincts. But I wouldn't rule out neighbors. Sometimes someone else's cat is so sweet and adorable that others can't help but want to take them in. But in most cases if they see that you are so distraught, it may make them realize that they already have a loving home and even though they may not personally hand him over, he may suddenly and mysteriously "reappear" at home soon after!
Still praying for your little guy and I'm sure he will return home soon - boys are notorious for galavanting this time of year and stressing out their mommies! Naughty things!
Remember to keep food and water out there for him and something with your scent all over it!