AFI, you need a big hug!
I used to have 4 kitties and one day we left for awhile and left the windows open--screened in casement windows (with a top and a bottom). Well, when we came back, one of the windows had fallen down (closed shut) and the screen behind it had been ripped open and my favorite kitty was gone. I was so heartbroken and sad. And the poor guy was out in a very urban area. He had been outside a lot before--when I was in college, we lived in the country, so he got to roam around a lot. But never anyplace where there were lots of cars and people.
We called for him, put up signs, visited shelters, and finally, had pretty much had given up on him. When almost a month later, about 2 in the morning, we hear this wailing at the back door. He had returned! And, he talked and talked to us in his meow voice for hours. Couldn't tell whether he was yelling at us for being so dumb to leave the windows open or whether he was telling us of his adventures in the big city. I was just so happy to have him back in our life.
We never did figure out whether someone had just taken him (by cutting the screen and then he escaped from them) or whether he had gotten trapped between the window and the screen when the window fell down and had then clawed his way out.
So, I don't want to get your hopes up too much, but the return of a kitty is possible. I will cross my fingers and say a little prayer for you and your kitty.
And, please, check all shelters in your area, the police department, and the lost and found ads in all of the local papers. Putting up signs with his picture and putting a lost ad in the papers are good ideas also. And ask the neighbors. You never know if someone might have seen him around. And, check around the area--particularly locked garages, apartment building basements, and sheds. It's possible that your kitty could be locked in someplace. I say this because, a few years back, we had a stray hanging around our house for a few weeks and then completely disappeared--seems that she got locked in the neighbor's garage when they left for a week's vacation. Once they came back and opened the garage door, she scampered out--skinny, but still alive. Right then and there, I vowed to find her a no-kill shelter for a home. And, I succeeded.
I feel for you, AFI. Just talking about this brings back such wonderful memories of my crazy cats (can't have them now because my daughter is deathly allergic). You must miss him so much.

Tested made this fabulous set for me!!! Isn't it great?