When news broke last week that Prince Harry and Meghan, Duchess of Sussex, would be stepping aside from royal duties, fans of the celebrity-focused podcast “Who? Weekly” thrilled to discuss it: Where would they live? (Canada? California?) Would they get jobs? What did the queen think? Their ideas — and inside jokes — played out across several of the podcast’s Facebook fan groups.

Podcasts, as Jamie Lauren Keiles wrote last year in The New York Times Magazine, have given rise to fan universes once reserved for popular TV shows. And many of those fandoms live on Facebook. Groups for podcasts like “Crime Junkie” and “Shameless” have ballooned to tens of thousands of members, and in some cases more than 100,000. And those are just the primary fan pages.

When a show’s following is particularly rabid, fans break off into smaller splinter groups, allowing for more focused discussions. “Forever 35,” a popular podcast about self-care, has spawned 99 offshoots. “LadyGang,” a celebrity and lifestyle podcast, has subgroups clustered by region, interests and goals, such as getting out of debt or keeping up a keto diet. “Who? Weekly” fans have at least 20, including “influWHO?encers” and “The Who?k For Less.”

The growth of these groups represents both a cultural shift and a strategic one. In 2017, Facebook saw that users were posting fewer personal updates, and younger users were flocking to Instagram. The network could no longer rely on friend suggestions for growth. Groups, on the other hand, might encourage connections between strangers with common interests, and become places to engage in endless conversation online.