An iPad will retain its serial number, it doesn't change - it will be able to be used with a person's iTunes and the iTunes store.
If your iPad has been stolen then Uunless you had Find My iPad enabled on it then you won't be able to try and locate it - it can't be located via its serial number. If you did have it enabled then you could try locating it either via http://icloud.com on a computer or the Find My iPhone app on another iOS device - but that will only work if it's connected to a network and the device hasn't already been wiped and/or Find My iPad disabled on it.
You've reported it to the police ? You should also change your iTunes account password, your email account passwords, and any passwords that you'd stored on websites/emails/notes etc.