You can now enable Youtube Search API to add youtube searching.
First you need to get your personal youtube API key from : https://developers.google.com/youtube/v3/getting-started
Once you got that key (ex: AIzaSyBsdbcJ1YhvG64t9n541CqOHcXiXXXXXX), you can update your chat config and set that key.
Now, anytime you press the youtube button, you will be prompted to enter the search keyword.