Facebook Groups are very popular in the country I live. (Reddit is too American-centric to have ever really caught on.)

I'm in groups on legal stuff (19,000 members), boardgames (16,000 members), family stuff likes activities for kids (9,000 members), roadtrips (5,000 members), camping (9,000 members), food (41,000 members), dog lovers (14,000 members), and a general city group (150,000 members), a group for my neighborhood (22,000 members), a musicians network (3,300 members), pens (montblanc, etc; 8,800 members)

Most those groups are just for my city (i.e. the dog lovers is just for dog lovers in my city).