How to Tag People in Comments on Facebook
Facebook tags give your friends a heads up when you're mentioning them in a post on the social networking site. Use the tags feature to talk about who you're with at the moment, include friends in a post about future plans or just tease someone in a comment. Whenever you tag a friend, Facebook notifies her; the entire post in which she is tagged also appears on her Facebook wall.
Click on the "Write a comment..." field at the bottom of any Facebook post to which you have privileges to comment. You are permitted to comment on your own posts and posts on pages of your confirmed friends.
Type the "@" symbol and the first few letters of the name of the person to be tagged.
Select your friend from the list that Facebook automatically generates based on the letters you typed. Click a friend's name once to select her.
Repeat Step 2 and Step 3 for each person you want to tag. Regular text can also be inserted before and after each tag.
Hit the "Enter" key to post the comment.