Make a poster with a photo and the chip number and take to the vet clinic. When I worked at Doha Vets we reunited quite a lot of people with their cats and dogs this way. The police will accept the chip as evidence of ownership, this is important as friendly cats sometimes get sold at the Souk for a lot of money. As awful as it is, you also need to go to the Souk animal market every day, if it is a long haired cat they may try and sell it if they found it.
At my clinic, when people brought in a new pet, we always scanned it for a chip to make sure it wasn't lost or stolen.
If you offer a reward you may get lots of calls but be careful of people trying to take you for a ride.
Good Luck, JJ