Sorry to hear about your MacBook. I found a couple of resources that might help with locating the serial number for your MacBook.
If you registered yoru MacBook when you purchased it, you can view the serial number in the Support Profile of the Apple ID you registered it to:
Although Apple does not have a process to track or flag lost or stolen product, you can use My Support Profile to find a list of serial numbers that have been purchased or registered with your Apple ID.
You can find the full article here:
If you never registered your MacBook with your Apple ID, you can also find the serial number on the packaging:
Thank you for using Apple Support Communities.