You can try this:
UIGraphicsBeginImageContextWithOptions((CGSize){ 1, 1 }, NO, 0.0f);
UIImage *transparentImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[self.seekBar setMinimumTrackImage:transparentImage forState:UIControlStateNormal];
[self.seekBar setMaximumTrackImage:transparentImage forState:UIControlStateNormal];
[self.seekBar setTintColor:[UIColor clearColor]];
Hope it helps :)