Hi everyone, we are currently working on a problem with our chat client. WE are working on this as quickly as we can and once this issue has been resolved you'll have your friends back. In the meantime I apologize for the inconvenience.
Your friends lists should be coming back up now. I would suggest restarting your game client if they are still missing. This fix has a rolling effect so if you are still missing your friends just keep trying every 10 minutes or so.