My iphone is lost can I track it if I have my serial number?

No. If you did not have Find My Phone turned on/activated, there is no way to track your phone other than physically looking for it.

sir i have loose my i phone 3G and i am trying to track my set it's also shows on map but i can catch that guy so. please suggest me how can i block my i phone thanks.

what if I get the authorities involved?

If you have been activated Find My Phone

or mail me.com

Contact your support me.com

http://www.apple.com/ru/support/mobileme/

live chat, describe your problem

The authorities cannot track iPhones either if you didn't setup the feature.