If your NOOK is lost or stolen, contact Customer Service by clicking here and using any of the Contact Us options in the lower left corner to unregister the device from your bn.com account. After you have spoken with Customer Service, we recommend signing into your Barnes and Noble Account and changing your password as well as removing any payment methods until this is completed.

Locate Serial Number on bn.com

Even if your NOOK is lost or stolen, you can still obtain your serial number from your bn.com account by visiting your Manage Devices page. If you are not signed in, sign to the account registered to your device. 

On that page, your NOOK will be displayed with the device type, an image, and the Serial Number displayed.