Just a quick heads-up for those who don’t know yet: there is closed group “Astronomers” on facebook. It is by invitation only, ie some existing member must add any new member. You must have an fb account to be added.
The group has about 4,000 members, most all professional astronomers from around the world.
There is some interesting discussion going on in that group and some useful info being passed around.
The closed group feature seems to work well for some combination of intensity of topic focus and size – not too small, not too big.
‘fraid I wouldn’t tell how to monetize the feature though.