YouTube (iOS 7)

Use this link to launch the YouTube application

vnd.youtube://

Application homepage: vnd.youtube://
iTunes link: https://itunes.apple.com/us/app/youtube/id544007664
HTML Link example: vnd.youtube://
Native application URL string example: vnd.youtube://
Extended example:
Tags: You tube YouTube video videos 7

Just do 

vnd.youtube://

and you'll be fine