The ongoing problem YouTube faces is that although the service is increasingly interactive, it seems the mobile side of the interaction is less than that of other social media networks.
Recently YouTube changed the rules of their usage policy to require any user wishing to comment or interact in anyway with any of the uploaded content, to have a Google+ account. If you have a Gmail account, you have one of these automatically. Similarly, if you have a YouTube account, it’s just a couple of clicks to activate yours, and this is where the start of that interaction begins.
Take a look at the video for a shirt explanation and walk through for how to do this on your phone or tablet.