You're code's going wrong because, although you're checking if you can open the youTube URL more or less correctly, you're then just opening a web address, which will always open in Safari.
This is the code I've just used, which is working for me. You might want to modify the else statement if you want to fallback to using a webviewcontroller as this will open Safari if the youtube app isn't installed.
NSString *channelName = @"TheNameOfTheChannel";
NSURL *linkToAppURL = [NSURL URLWithString:[NSString stringWithFormat:@"youtube://user/%@",channelName]];
NSURL *linkToWebURL = [NSURL URLWithString:[NSString stringWithFormat:@"http://www.youtube.com/user/%@",channelName]];
if ([[UIApplication sharedApplication] canOpenURL:linkToAppURL]) {
// Can open the youtube app URL so launch the youTube app with this URL
[[UIApplication sharedApplication] openURL:linkToAppURL];
}
else{
// Can't open the youtube app URL so launch Safari instead
[[UIApplication sharedApplication] openURL:linkToWebURL];
}