Hi Pinkcandy!
When one of my cats went missing I created a poster on my computer, including his photo, printed it off and photocopied it then stapled copies onto telegraph poles within a half mile radius of my home. I also contacted the local Cats Protection, the RSPCA, etc....and even contacted my local council to enquire whether his body had been found (it's their duty to dispose of dead animals on the roadside).
But I was SO glad that I'd written my phone number (and postcode) on his collar, in indelible ink, as FIVE WEEKS after he went missing I had a phone call from someone who'd been feeding him for a month (though he wouldn't let her near enough to read his collar until the end of that month!) - and, looking a little thin but otherwise healthy, I brought him home.
So don't give up - but if he's not wearing a collar with your phone number on it, you may need to advertise more widely. Why not try taking a photo of him (if you have one) to your local newspaper...sometimes they're only too pleased to write a little article, especially if there's a photo attached!
I DO hope you find him safe and well.