Just look at the active members at the bottom of the page. It'll tell you how many people are supposedly active and online at the current time. If it says 18 members, count how many there are there. If you count 16 names, then two people who are Invisible are online.
Yeah I know, that's so funny. One time this guy was like "No, I won't but the last two £250,000's". And then I decided to get them, and that's when I won that £20. I told him to get them, but he didn't listen.