You can't. Unless you set up MobileMe / Find My iPad on it before it was lost/stolen, then no, there isn't any way to locate it. If you did set up MobileMe on it then you could try locating it either via me.com on a computer or Find My iPhone / Find My iPad on a another device - but that will only work if it's connected to a network and the device hasn't already been wiped and/or MobileMe disabled on it.
If you think that it was stolen then you should report it to the police. As a safety precaution you should also change your iTunes account password, your email account passwords, and any passwords that you'd stored on websites/emails/notes etc.