I lost my Apple Watch how can I trace it?

If your Watch is lost or stolen

The easiest way is to go to the Find My app on your iPhone or go to icloud.com and log in. From there, the app will on the lower corner have a list called Devices, which you'll need to give a click. From there, it will give you a list of devices. From there, Find My should give you the option to

1) Play Sound to help find it if you think you're nearby or others looking for it are nearby.

2) Directions to its location

3) Notifications (to help notify you when it's found)

4) Mark as Lost

5) Erase (as a last resort)

Knowing you lost it while on vacation I would recommend marking it as lost and then using directions and notifications to help ensure you are notified when it gets found and to help make it easier for you to recover it, should a good Samaritan help you out.

Best of luck!