How can you send message on YouTube?

You can send a message on YouTube by using the private messaging system provided to each user. As long as a user didn't block you on YouTube, you will be able to send messages to the user you wish to send a message to. To access the private message feature, you should look for the "Inbox" link once you login to YouTube when you drop-down the bar under your username on the top-right corner of any YouTube page.