Q: if i lost my ipod how am i supposed to find the serial number..???

See here: iPod: How to find the serial number

Otherwise, head to Edit -> Preferences and then click on the Devices tab.  Hover your mouse over your iPod's backup and it's serial number should pop up.

B-rock

I'm not sure why you need the serial number.

Change your iTunes (Apple ID) password along with any other password that was stored in the iPod.  If any passwords are associated with credit cards, contact the CC company and get your card replaced (with a new number).  If any passwords are associated with your bank or any savings institution, contact them also and discuss approprate action with them.

The "Find my..." function is pretty much useless if the device is in the hands of a thief.  All that is necessary is for the thief to connect to any computer with iTunes and "Restore as new."

The only real protection you have is with the personal information on the device rather than the physical device itself.  This requires action before the device is lost/stolen.  Something as small as an iPod should have a strong 8-digit (or longer) password AND be configured for automatic wipe in the event of ten consecutive incorrect password entries.