I have created the chat room for magento. I would like to invite top users of magento tag. How can I do this?
If those users are not already involved in "chat", then there is (by design) no direct way to do this unless you are a moderator, as we do not want users bugged unless they want to be there. If they are on chat, you can request them individually, but please don't get carried away there. Where there is context you could also add a comment in the Q&A site "we could discuss this more in chat [link]"; however, again: do not go and spam everyone with a link - that would be... unappreciated.
We are also considering beefing up our relationship of rooms to tags, which would allow us to do a very targeted display of on-topic rooms, so the users could see the room naturally in the Q&A site.