Find my also only works if the iPad is visible....such as on wifi or the cellular network. Wifi iPads are very easily wiped without ever being seen. As folks have stated, if it was passcode locked, then your data is very much more secure, if it wasn't passcode locked, then a bad guy could have theoretically nosed around for info before wiping it (general impressions are that most stolen devices aren't stolen for their content, rather themselves..so most thieves' goal is to wipe it so they can resell it)
As a precaution you can change any password entered on that device, e-mail, apple ID, etc.
You will also want to register the theft with the police (which I'm sure you've already done)
In most states, if you've registered it as stolen and you ever come across it, you can reclaim you merchandise (long shot at best but has happened)
You can also keep an eye on local pawn stores, craigs list, the paper, etc.