React is worked on full-time by Facebook's product infrastructure and Instagram's user interface engineering teams. They're often around and available for questions.
Many members of the community use Stack Overflow to ask questions. Read through the existing questions tagged with reactjs or ask your own!
For longer-form conversations about React, we've set up a discussion forum at discuss.reactjs.org. This forum is a great place for discussion about best practices and application architecture as well as the future of React. If you have an answerable code-level question, please post it to Stack Overflow instead.
In the forum there's also a category for job posts and a category for discussion of our weekly meeting notes.
Many developers and users idle on Freenode.net's IRC network in #reactjs on freenode.
For the latest news about React, follow @reactjs on Twitter. In addition, you can use the #reactjs hashtag to see what others are saying or add to the conversation.