This method wil only work if you had signed into your phone with your goolgle account.
You can use Android Device Manager to find its approximate location on a map and when it was last used.
1. Sign in to your Google Account on android.com/devicemanager .
2. If you have more than one device, click
the arrow next to the device name to
select a different device.
3. Android Device Manager will show you
the approximate location of the device
You can locate or ring it by searching for "find my phone" on google
If this fails you can go to your network service provider and report you phone stolen, if the person who found it, used your sim card, they might be able to help, but the process is very long and might prove expensive.
when you do find it or buy another android phone install, Avast Anti-theft it will help you next time you lose your fone.