The only way I know how to add friends is if you go to your room, and the person sign all the way on the bottom right. Click on it and it should say Visit a random player. Then you click visit, and when you get there, there's another button in the same place as the person sign that says add friend. If you want to get out and go back to your room then press the button all the way at the bottom left. You're Welcome.
Comment found on Project Makeover: How to add friend