The Pluspora pod is operated and principally populated by Google+ refugees. As of 13 October 2018, pluspora.com - increased membership from perhaps 100 before the G+ termination announcement (October 8) to 5500 within a few days.
Numerous Google+ users actively use the system.
Minds has a "Google+ Refugees" community of 217 members. The site is a mix of public feed and groups (analogous to communities on G+) a bit token system linked to an e-currency allows the community to self-fund and content providers may be able to monetize their efforts. Some will find the token system disconcerting, but it is not mandatory for basic use of the site. There are hundreds of established groups of varying quality, just like on G+, or it is simple to set up a new community and wall out the barbarians. Content can be posted to a group OR publicly. All group posts appear in the public stream.
/r/GooglePlus is a general-interest Google Plus forum not specifically oriented at refugees. Moderators have not responded to inquiries from Dredmorbius (/u/dredmorbius at Reddit). 6,681 subscribers as of 19 October 2018.
/r/GooglePlusRefugees is a general-discussion forum. 174 subscribers as of 19 October 2018.