It's very easy to tell when a bunch of people are in Organia.

Even if you have no power to locate people (and there are such things in the game), people in Organia can't receive tells.

It's an easy way to figure out who is there.

"Tell Patick I'm coming for your soul."

If Patick can't hear you, try someone else. If those that can't hear look like a group... they are probably in Organia or one of a very limited other number of places that prevent it.