How worrisome. Hope you find him soon! Hopefully he found a nice warm and dry shed to be in, with an old lady throwing him food, who just hasn't seen flyers or anything yet.
Definitely go to the shelter and see if he's there with your own eyes. At our shelter a lady that lost her dog called 4 days, every day she was told no. Finally she went up there HER DOG WAS THERE THE WHOLE TIME! They said they were overloaded and he hadn't been processed.
That. Not only worry of "not being processed", but what one person sees, and what another person sees, may be different. One person says dark brown, the other says it's black, so they don't think they have a dark brown dog, etc.
Though, with Norris that's kind of moot. But, you know... lol