How to report lost ipad by serial number to apple

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

See the information in the support document that you linked here from. That provides you with a link with information on how to track your device. Apple does not provide services for this, with the exception of providing the link to log into iCloud to trace it. They do not track devices, as it states in that support document.

Apple gives you the tools (Find my iPad). I'm sure they don't want to have anything to do with lost/stolen devices. You can report it to Apple. They'll probably tell you to do exactly what the article says.