My brand new unpacked Watch was stolen. I have the receipt and the serial number. Can you help me find it?

It can't be traced with a serial number,if the watch wasn't paired then you can't track it through the findmy app either;

If your Watch is lost or stolen

MankaPaleva wrote:

My brand new unpacked Watch was stolen. Is there a way to trace it with the serial number?

Tracking-by-serial-number would be a catastrophic security and privacy breach, and would immediately be massively abused by abusive exes, thieves, crooks, and miscreants. Thefts, injuries, and worse, would result.

Best you can do is a police report if that’s an option for you, and reporting the IMEI as stolen to your carrier if a cellular Watch.

MankaPaleva wrote:

Tracking with serial number is technically possible. I wonder how this can be an issue if it is done when someone can prove to be the owner (receipt, credit cart, and ID) and is requested by him? Reporting to police is not very efficient, I haven’t heard of many successful stories with phones and other mobile devices.

Contact local police, and/or contact the carrier and blacklist the IMEI for a cellular device. Nobody here wants to or even can investigate and adjudicate the claims being made here, nor will anybody here retroactively insure and reimburse. You have a crime of some sort. Contact police.

The bottom line here is that Apple don't get involved with lost or stolen watches.