Established G+ Exodus Communities
G+ Diaspora Communities
pluspora.com - increased membership from perhaps 100 before the G+ termination announcement (October 9?) to 5500 within a few days afterward (effective October 13).
mewe.com community "Google Plus Refugees" has 124 members as of October 9. community "Google+" has 20 members.
on Cake.co there is an interest category called "Google" with 189 followers. Recent posts pertain to the demise of G+ but the category also tracks other Google-related matters such as the Pixel 3 and other hardware, working at Google, etc.