The thing is that you cannot check if members are online in the game by checking on the site, these two parts are different from one another.
Sure, if a member is logged on the site they might be on the game as well, but for most part this is not the case. If you want to send messages on the site or see if someone browse the forum you are able to do so by looking at the bottom of the forum index(the main page of the forum at the bottom). It shows all the online users at the time when it comes to the forum.
If you want to see if a certain user is online in the game though, you must have them on your friendlist, and in that case they will show up on your list as "Online". That's the only way for ingame.