Try to take a picture of the found cat.
Join the group “Gevonden katten Vlaams- Brabant (B)” on Facebook. There you reach hundreds of people immediately.
Once you join the group, post a message with the following information:
Also include whether you took it to the vet, notified the police or a shelter and took the cat in.
Also report it on the website https://www.vermistekatten.be/kat-gevonden/
Always put an update, in or below the message, if the owner has been found, if the animal has gone to a shelter or the police so that the message is not shared further and it can be deleted or delete the message yourself.
Some additional tips if you have found a cat