Current discussion and other activity is on the Nyancoins reddit: reddit.com/r/nyancoins/
Bitcointalk Forum (Thread started 5 October 2016). There are several older ones, but they contain incorrect out of date information.
Facebook page which was set up by the original developers, has not been used since 2014. However anyone can post to the page, so not entirely useless.
Updated 16 November 2017.