Find my iPod Touch (iOS 4.2.1 and greater) - http://images.apple.com/ipod-touch/icloud/#find -
The following conditions ALL have to be met:
1) You have the "Find My" activated BEFORE you lose the device.
2) The device is turned on.
3) The device is able to connect to a registered wifi connection (iPad, iPhone, iPod Touch) or data network (iPhone, iPad).
4) The device was not restored by a finder of the device (if it was really stolen then the thief has probably restored it).
If you have activated the "Find My" feature, go to https://www.icloud.com or use the Find My iPhone app - http://itunes.apple.com/us/app/find-my-iphone/id376101648?mt=8
Setting up iCloud (requires iOS5) - http://www.apple.com/icloud/setup/ios.html - includes activating the 'Find My' feature.
Frankly in the case of a stolen iPod this almost never works. Report it to the police. Change passwords on accounts.
Kappy's missing idevice recommendations 09/2012 - https://discussions.apple.com/message/19569712
If your music was purchased from the iTunes Store you can dowload it again. It should all be on your computer anyway, or on the backup you maintain of your computer. It it isn't on your computer and didn't come from the iTunes Store then you'll have to recover it from whatever original source you used.