If I look at who I know that is still using fb it is almost exclusively older people. I'm 33 and deleted my fb account, almost every person I know younger than me either did the same or was never on in the first place. I see this being huge for older adults who are divorced or widowed, those are the people still using fb and I think would be happy to use this service.
Go to Facebook Marketplace and search for wedding dresses. It'll show you recently divorced females in your area. From there you can filter by size.
Hacker.News.