You can of course report on Nextdoor, but not everyone is affiliated with it. Facebook also does not usually have the desired effect. What then ?
According to article 5 of our Civil Code, every citizen must, if he does not know who it belongs to, report an object to the municipality.
This can be done in a number of ways: taking the object to the Lost and Found Counter (Vestdijk 147) or to a police station; calling 14040 is of course also a possibility.
But the object can also be registered via the websites https://www.verlorenofgevonden.nl/melding?lang=en or https://ilost.co/en/. On these sites you can also see if your lost item has been found and reported.
More info (in dutch) on the website of the municipality: https://www.eindhoven.nl/stad-en-wonen/stad/vrije-tijd/gevonden-of-verloren-voorwerpen.