I suppose that means that you did not have it set up with the "find my iPhone" app?
http://www.apple.com/uk/icloud/find-my-iphone.html

If you are trying to do it after the event you are probably going to have little chance unless you have any remote access technology already installed on the device.

Have you tried ringing the number? The other thing for next time is also something like the "Return Me" app, so that on the locked homepage it gives contact details.
https://itunes.apple.com/gb/app/retu...316997752?mt=8