Reddit Atheism is the largest online community of atheists, with over 2 million members.
There are very few rules; it’s mostly just a group of atheists talking to each about whatever they want (most of them choose to talk about ways they think religion is bad).
Reddit Atheism recommends a number of other Reddit pages, like r/streetepistemology.
Reddit Atheism has a “Coming Out” page which they take very seriously and begins:
“This page is meant to help younger atheists who might be considering coming out or already have come out to their parents.
“Please please read this page and submit to the community any questions you have (or even just your thoughts). There are many people here who were once in your shoes who can give helpful advice or at least understand your situation.”