i lost my ipod in public and i don't think that it's connected to wi_fi so what should i do ??

In order to locate a lost iPod Touch:

• You have to have an iCloud account
• You have to have set up 'Find My iPod' on it before losing it
• It has to be on, not wiped, and able to connect to a network.

If any of these conditions is not met then it is not possible to locate it.

I'm afraid that is what you will have to do - I hope you find it.