Any good sites/ideas to help find a lost cat?

[Nada Chance]

Make sure you've let all the neighbors know the cat is missing, and left a flier with all vets for a several mile radius, too. Newspapers often run lost-and-found ads free for a few days.

There are usually SEVERAL animal shelters in a city, plus rescues. Make sure to google animal shelters, animal rescues, etc. in your city and call all of them. Ask if they know of any other place the cat could be, too.

Many lost cats are found in the neighbor's garage a few days later. They sneak in, the door goes down, the cat is trapped. I recommend going a few houses down the street each way and across the street and asking them to check their garage or crawl space if they have been accessible in the time frame the cat has been missing.

Finally, head here https://forums.craigslist.org/?forumID=26 if you want some more advice. It's a pets-and-animals discussion forum and it has rescuers, animal cops, vets, breeders, trainers, and a bunch of people that just love animals. They can help. :-)

In the meantime, make sure you have at least one item of your clothing, that smells of you, outside your house. Front and back would be best. Cats can get freaked out and "stupid" and not realize that it's their home. The clothes help the cats ID the house and stick around.