Aw, I sympathise so much. Mine was missing for 8 days and it was one of the worse weeks of my life.
Don't give up hope yet though, they so often stroll in like nothing happened!
Put their litter tray/bed/blanket/contents of your hoover outside so that they can follow their scent home.
Put stinky wet food around the boundary of your property.
Post on Facebook local pages, Petlog, community websites, gumtree etc with a photo, date last seen and location, and your contact details. Contacting social organisations for the elderly including church groups are often very helpful and kind.
Print posters with a photo, date last seen and location, and your contact details.
Put posters/flyers with above information through neighbours doors asking them to check sheds, garages and out buildings.
Contact all local vets, RSPCA and PDSA asking them to keep an eye out.
Go out at night when it is very quiet and still to call for them and listen. (this was what eventually brought my cat home).
Knock on doors with your flyers and put a human face to your missing cat. Neighbours are often more likely to check their sheds of help you look when you’ve spoken to them.