If you go to your alliance it says last played on a player. If it has a few days ago it's green, yellow then red, but if they are online right now it should be blue or a different colour. If they are on now it will say the last time they logged in, so if I look it says last played,
12:54 PM 0 ays ago
they send a message to you at 1:00 PM
You check when they were last on and still 12:54 PM 0 days ago
So if they are online the circle thing should be blue so you can send a message and expext a fast response.