Did you brother choose to "Use Find My iPhone" when he was setting up the phone, and kept location services on?
If so, then once the device is connected to the Internet with location services on, then it will show up on mobileme.com.
But as long as the thief keeps location services off you won't be able to find it on the map.
Basically you just have to keep checking until you see it.
Do you have an iPhone or iDevice?
Download the Find My iPhone app on any of your devices, and log in with his account. Chance are it will say location disabled.
Toggle on the button that says email when found.
I'm pretty sure the email will go to or brothers Apple ID email address when the device is found.
Hopefully the thief does not know too much about iPhones....because if he does then you may never find it. I'm really sorry this happened to your brother.