How can I find a lost Apple Watch

Hi

If Activation Lock was enabled on your watch, you can mark it as missing either via the Watch app on your iPhone or via iCloud.com.

Instructions and further information about this feature are available here:

About Activation Lock on your Apple Watch - Apple Support

Note that Apple Watch cannot be physically tracked / located in the same way as some other Apple devices. I'm afraid it is not presently possible to track, find or recover your watch via any Apple service (with or without the serial number and regardless of whether or not Activation Lock was enabled beforehand).

If you had added cards to Apple Pay on your watch, you can also call your card issuer to advise them of the theft.

Also report the theft to your local law enforcement / police.

Depending on how you had configured your watch and what the thief has done with it, you may also wish to try calling your iPhone number from another phone, in case the watch is still nearby and rings (mute your iPhone using the side switch).