How do i find a cat thats been lost for a while?

Sounds like they are being trapped. If you let them outside and a neighbor doesn't like cats, they have every right to trap them according to the law. Hopefully they took the cats to the local animal shelter. If so, that is where you would find them. If you have a cat killer in your neighborhood, then it will only stop once the person is caught. Wouldn't you rather keep your cats inside even though they fight than to lose them? ( may be be a few blocks away, cats roam)