Are you entering the command correctly? To play a video, type: /youtube [link]
To bring up search criteria on the right hand column of chat, type: /youtube [keyword(s)]
Omit the brackets I have there when you are entering the commands.
Here is a screen shot showing me searching for the video (first line of text). You can see on the right column, videos related to that name have been pulled up.
In the second line of text, I used the link to the video to start it.
Example (see attached image):