I cant no longer use the find my iphone app can you please help me? I lost my iphone :(

Unless whoever stole your phone knows your Passcode, Apple ID and Apple ID Password, they CANNOT turn off Find My. Your phone may not be tracked if it is not powered on or connected to a network. And a phone which has not been powered on for 24 hours no longer shows last location in Find My.

See this link about what to do if your iPhone is lost or stolen --> If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

What has more than likely happened is that your iPhone is either turned OFF and/or ran out of battery charge. Without power your iPhone will not be able to report its position. Also note that without an internet connection, it will not be able to report its position either. If the thief erased the iPhone because s/he could not get past the passcode then the iPhone will not report its position.

Axel F.