Interaction with fan on your facebook page

You can only tag your fan to a post when they comment on that post first. As you can see in the picture below. There are two fans that interact with my page post. One fan just liked it and another fan commented on it. For the fan that like my post. I cannot tag him into my comment. And for the fan who commented on my post, I can tag him or mention him when I comment on that same post.