Maybe your path is wrong, it should be path to a file inside the app's bundle.
Add your sms_alert_circles.caf
file to your xcode project. Check that file is in "Copy Bundle Resources" list in "Build Phases" of project. Then change following line:
NSURL *fileURL = [NSURL URLWithString:@"/System/Library/Audio/UISounds/Modern/sms_alert_circles.caf"];
to
NSString *soundPath = [[NSBundle mainBundle]
pathForResource:@"sms_alert_circles.caf"
ofType:nil];
NSURL *fileURL = [NSURL URLWithString:soundPath];
Also you can try to use AKSystemSound library to play sound via almost one line of code.