My iphone has been stolen and it says it is offline on find my iphone?

Could you please tell me a good and free website on how to gps track it or tell me some other helpful advise?! I know it was stolen because I sent a message in lost mode and someone called on their phone saying i need to pay to get it back and now they won't answer my calls anymore! Please help me I already contacted the police and they aren't doing any good so please assist me

Yes why not, first of all just get the bill of your iphone and see the imei no of your phone or if you don't have the bill, go to the apple store from where you bought your iphone and ask them for imei no of your iphone ( they usually keep copy of bills ) and once you get your imei no, go to the nearest police station and submit them the imei no, and they will find it in no time, trust me i lost mine but got it within 3 days with the help of police

You accually called the police because of your phone lol don't waist there time.

Thank you so much…

If you set up Find My iPhone on your phone before, you can try to locate where it is with this app. Just go to https://www.icloud.com/...cloud.com/ in your web browser. When you log in, Find My iPhone will immediately begin trying to locate your phone if it is online. If it is offline, you can try to enable Lost Mode and others, learn more here: http://www.wikihow.com/Find-a-Lost-iPhone
If it does not work, it is better for you to contact your service provider and phone provider and see if they can help.
To prevent your new idevice from being stolen or lost in the future, I suggest you apply some free anti-theft apps like iLostFinder ( http://ikeymonitor.com/free-apps ) except set up Find My iPhone/iPad/iPod in iCloud on the device. It will take pics of the thief or finder when she/he tries to open your device with a wrong pass and then send the pics to your email etc. Hope it helps.