Is it possible to disable a lost iPad?
Did you have Find My iPad activated via the iCloud settings on your iPad? 

If so, then you will be able to do any of the following on your iPad:


locate it on a map
send a message to it
play a sound on it
remotely lock it
remotely wipe it


Just for the record, when you enable iCloud, options 2, 3, 4 and 5 above are automatically enabled. 

If you have Location Services turned on, Find My iPad can also help you locate your iPad on a map as long as it's connected to the Internet. 

If you had this activated, or aren't sure if you did, then follow these steps:


use the Find My iPhone app on an iPhone or another iPad or visit icloud.com/find from a computer with a web browser.
Log in to your iCloud account (this may or may not be the same as your usual Apple ID).
Once you're logged in, see if your missing iPad is listed under My Devices.
If it's listed, then that means it's been set up for Find My iPad (a good sign).
Now, if it's currently connected to the internet, you have two possibilities:


if you had location services activated on the iPad, you should see its location come up. Clicking/tapping on the icon will display the Actions option and tapping on this will give you the following three choices: Play Sound; Lost Mode; and Erase iPad.
if you didn't have location services activated on the iPad, it will display a message like "Online, no location available". In this case, clicking/tapping on the iPad icon will give you the following four choices: Notify When Found; Play Sound; Lost Mode; and Erase iPad.

If it's not connected, it will display as being "Offline". Clicking/tapping on the iPad icon will also display the following four choices: Notify When Found; Play Sound; Lost Mode; and Erase iPad.
Select the option you want.


For the benefit of others, there are other services to achieve what you want. However, all of these involve installing third party software on the device (and since you're asking the question it's safe to assume you haven't done this).

Regardless of whether you have Find My iPad activated, this would be a good time to reset your passwords for any online services, email addresses, etc. However, in doing so, you would be best to change your email passwords first to minimise the risk of any password reset info being intercepted on the iPad.