Lost my iPad mini 2

You can't by its serial number, unless you had Settings > iCloud > Find My iPad enabled on it there isn't any way to try and locate it. If you did have it enabled you could try locating it either via http://www.icloud.com on a computer or Find My iPhone app on another iOS device - but that will only work if it's connected to a network.

If you think that it was stolen you should report 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.