If the iPad was running iOS 7, the thief will not ever be able to use it.
iCloud: Find My iPhone Activation Lock in iOS 7
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
What to do if your iOS device is lost or stolen
iCloud: Locate your device on a map
iCloud: Lost Mode - Lock and Trace
iCloud: Remotely Erase your device
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
Two things you can do to secure your iOS device:
1. Use a passcode lock on the lock screen, and set it to engage immediately. If possible even consider a complex passcode instead of the short 4-digit passcode. The passcode lock is the ONLY security feature to actually keep others from accessing your content.
2. set up an iCloud account (even you do not use it for anything but Activation Lock), and enable find my iPhone so that iOS 7's Activation Lock is in effect. Activation Lock cannot be bypassed by erasing/restoring the device. Even if you do not want to use any other iCloud feature, you can simply disable everything but find my iPhone under the iCloud account's settings.
And, keep a record of your IMEI number and serial number somewhere so you can request blacklisting of the device by your carrier (if they offer such a thing - major USA carriers now do).
Honestly, I would never count on being able to recover or find a lost or stolen device. Even with iOS 7, find my iPhone is easily disabled by anyone (they just need turn your phone off). Remote tracking is really not a security feature, it is a convenience feature to find a lost device, not track down one stolen by someone. The important thing to do is AL, as it makes the device unuseable by anyone else, and passcode lock, to actually secure your personal content from unintended use or view. Secure your content, render the device useless to whomever has it, and then be prepared to get a replacement for your own use should your current device go missing.