Apple (and no one else) can not assist (with serial number or iCloud) in finding a lost or stolen iPad.
Report to police along with serial number. Change all your passwords.
These links may be helpful.
How to Track and Report Stolen iPad
Reporting a lost or stolen Apple product
iCloud: Locate your device on a map
Report Stolen iPad Tips and iPad Theft Prevention
How to recover a lost or stolen iPad
How to Find a Stolen iPad
What NOT to do if your iPhone or iPad is lost or stolen
Apple Product Lost or Stolen
Oops! iForgot My New iPad On the Plane; Now What?
If you don't know your lost/stolen iPad's serial number, use the instructions below. The S/N is also on the iPad's box.
How to Find Your iPad Serial Number
iOS: How to find the serial number, IMEI, MEID, CDN, and ICCID number
Find My has a few weaknesses, namely that your iPad needs to be on the internet to be traced. Keep it off line and it's untracable. Also a knowledgable person can wipe it and render 'find my' useless in a few minutes. It was meant more to find lost devices (remind you that you left it at home, for example) than to ever be a theft deterrant or recovery tool.
One of the changes that I've read in the iOS7 release is that the app will requires owner input to be deactivated. Which will be great, unfortunately too late to help you and countless others. (presuming of course that what was on the press release will be in the final release.
Losing your iPhone feels lousy. Thankfully, Find My iPhone can help you get it back. But if it looks like that’s not going to happen, new security features in iOS 7 make it harder for anyone who’s not you to use or sell your device. Now turning off Find My iPhone or erasing your device requires your Apple ID and password. Find My iPhone can also continue to display a custom message, even after your device is erased. And your Apple ID and password are required before anyone can reactivate it.
Getting a police report and getting it legally noted as stolen opens the door to you ever getting your device back if the police come across it in the future.