Is he the owner of yobit? If so, he's offline since April 30.
If that so, it's not a good news for yobit users.
When you have an exchanger, you should be around everyday. If you're that busy, you should either hire people to answer to support tickets.
If you send him a private message, it should also generate an email to him with the message, on the email he signed up at bitcointalk with, so he will get your message without having to log in.