Those are not easy to find, it's not really something they advertise and you need somebody to publicly catch them.

The only reason I know they do is because some of my friends working on mobile video games regularly complain they can't get some features because they are private while google and facebook do. They analyzed some apps to try to copy said features and realized the unfairness of their situation.

Those are lunch chit chats, not hard facts. But they got seldom reasons to lie.