Apple - iPhone 4S - Locate your missing iPhone with Find My iPhone - http://www.apple.com/iphone/built-in-apps/find-my-iphone.html
Note that these features require you have the "Find My" activated before you lose the device, and that the device be turned on, and able to connect to a registered wifi connection (iPad or iPad Touch) or data network (iPhone), and not having been 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/
If you haven't activated Find My Phone BEFORE it was lost, you can't locate it
Apple doesn't find or "block" iPhones. You need to contact your carrier ASAP to terminate service. Some carriers will put the IMEI number of the phone on a blacklist, but this isn't shared between carriers.
Contact your local police to report the theft. Not likely they will never recover it, but you might get lucky if the thief was run over by a bus just after stealing it.
Picture of the thief - Haha is the correct response... There is an app for jailbroken phones that claims to do that, but pointless. 99+% of iPhone thieves never use the phone - it's restored and put up for sale on ebay.