Earlier quoted context omitted.
Nextdoor is a private message board, which is an ideal environment for people who enjoy message boards and the type of conversations they engender, while the unit of content on Placewire is a photo. I believe this enables a different type of conversation and will engage a different set of users. I think Facebook groups are typically used at micro-local (eg. a city block) scale and it's perfect for sharing information…
In what sense is Nextdoor a private message board? I don't see Nextdoor as being more private than other social media networks. (Genuinely asking, not trying to shoot you down!)
In that it requires address validation. So "private" per se is wrong, sorry, but nothing within a community is intended to travel. Placewire is happily promiscuous. Thanks for the question.