We set ours up on the profile privacy settings. You have to choose where it is visible you are online to others.
For example you can set it so it shows you offline to someone randomly preving your profile. If it's set to on then everyone can see you are online and msg you. Alot of people seem to turn it off now as it gets annoying when random people msg you and you are say typing a msg.
Also it seems to randomly choose when it shows you online of it's own accord. Oh and it likes to shut down while you are using it lol
I think itshows you as online under your profile pic on your profile home page. Tho I just checked your profile and couldn't see it. But I am on my iPhone so it maybe that I'll check again on the laptop later unless someone else can confirm.
It also comes up on adverts I believe aswell as we had the same problem as you so I went through and turned most of them off.
If no one else jumps in this thread I'll check later and let you know.
X
your avatar on here.....right below it is IM button...if its green..i can press it and it allows me to send you a message. I do think you can change this in your settings if you want.