I lost my iPad

Did you specifically purchase an AppleCare+ for iPad. To my knowledge, it does not include theft and loss. You can purchase AppleCare+ Theft and Loss for iPhone. But not for iPad. If you have lost your iPad, there is no claim to file. You will need to purchase a new iPad.

The details of AppleCare+ are linked from this page:

https://www.apple.com/support/products/ipad/