Millions of people around the world are sentientists, in that they are committed to evidence and reason and grant moral consideration to all sentient beings. Many of them will identify as atheists, secular humanists, skeptics or free-thinkers who take non-human animal ethics seriously, but most of them haven't yet heard of the term "sentientism".
Sentientism is just a worldview, not an organisation. There's no membership (although you can declare yourself a sentientist here) and no rules (beyond the definition of sentientism itself). However, there is a wide range of global online communities and movements springing up around Sentientism.
If you find Sentientism interesting, we'd love you to come and join our main friendly, global community here. Anyone interested is welcome, whether or not you count yourself as a sentientist. We have people from around 100 countries involved to date – a mix of academics, activists, content creators, policy people and (the vast majority) interested lay people.
We also run a range of other online fora listed below. Join as many or as few as you like. Some focus on live conversation, others are more "post and comment", while others are good places to find resources.