I lost my cat, and I know who might have him, but I only have their Facebook. What should I do?

[Hand_of_Chaos]

Many cats have the feature. Its not that distinctive
YOU let the cat roam outside.
So what if someone has a cat that looks like yours, does not mean its yours.
If the cat is micro-chipped then that can prove its your cat but since you have no proof its you cat there is nothing you can do
The cops won't do anything since there is no proof its your cat