In January of 2016, my small indoor only cat was lost for eleven days. This is the story of how we found him, in hope that it can help you (although I hope you never need it.)
In 2014, my husband and I adopted two identical twin rescue cats, Fievel and Godzilla. They are sweet and gentle, and we love them very much.
That day in 2016, I must not have closed the door to our apartment correctly, because when we woke up in the morning, the door to our apartment was wide open. To our dismay, Godzilla was gone. We then called into work and spent the entire day searching for him in the woods surrounding our apartment.
We ultimately found him after 11 days (in January in Upstate New York.) These are the tips that helped find him.
1) Use a Rescue Trap: We found him by catching him in a Rescue Trap. We were able to borrow one from the rescue place that we adopted him from, but many rescue/adoption agencies might allow you to rent one. These are long, wide cages, that are open on one side, but sproing loaded so that the door shuts if there is enough weight in the cage.
We set the cage up next to the house, and this is ultimately how we found him. Because it was so cold, we had to check cage every half hour, and my husband found him at 2am.
2) Call the Shelters/Vet Offices: Call the shelters/vet offices are tell them your cat is lost, and to keep their eyes out. This is especially important if your cat is not micro-chipped, that you are looking for a cat if someone brings one in.
3) Use Social Media: We used facebook to get the word out and share pictures of our lost cat. Our local meteorologist is an animal lover and he shared facebook posts.
4) Tell the Neighbors: One of the differences between a lost dog and a lost cat, is that usually if a dog is loose, everyone knows he is lost and someone is missing him. However, there are so many stray cats, many people just think the cat is a stray. So make sure you tell your neighbors your cat is missing. WE probably got one call a day from neighbors (who were mostly seeing a stray that is not our cat) but we knew they were looking.
5) Use Wildlife Camera: We bought a wildlife camera that records motion and set it up near the house so that we would know if we saw him wandering about. There is a funny story where we tracked paw prints to an abandoned house in our neighborhood, and since it was snowing we set up a tarp over the rescue cage and would leave food there. The food kept disappearing, so we thought it was our cat. We set up the wildlife camera and pointed it at house, and it turns out we were taking very good care of a mouse in that house.
However, the wildlife camera showed up pictures of Godzilla around the trap before we were able to catch him, so that kept us from despairing.
6) Go out at Night: Godzilla is an indoor cat, and my understanding is that indoor cats when they get lost go into hiding, and then freeze. Because they are so scared, they are more likely to come out of hiding at night time, so try to search then.
7) Don't Give Up: Our cat was lost for eleven days. When we didn't find him after the first day, we feared the worst, but we kept looking. When we did find him, we rushed him to the emergency vet. He had some frost bite on his paw pads, and had lost 3 lbs (going down from 9 to 6 lbs) but was ultimately fine.
I'm so happy we kept looking for him, and I hope your find your pet too.
Please leave any other advice in comments!