Use this, and don't forget to put the delegate on your .h file, hope it works ;)
_mapView.userTrackingMode = YES;
- (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation {
MKCoordinateRegion region;
MKCoordinateSpan span;
span.latitudeDelta = 0.00001;
span.longitudeDelta = 0.00001;
CLLocationCoordinate2D location = _mapView.userLocation.coordinate;
region.span = span;
region.center = location;
[_mapView setRegion:region animated:TRUE];
[_mapView regionThatFits:region];
}