There is a community on Steemit called Atheism. I am a member.

Also, there is Atheist Republic. That's another Steemit community, hosted by the international organization of the same name: Atheist Republic. I am a member of this as well.

Both of these communities are very inactive, in fact I am the only one who has posted in either in a while, but at least they are here. Maybe I can elicit more interest in them.