> Curious, how many people do you need on a social network before you can find someone to talk to or before it is engaging enough for you?

I don't think that's a meaningful parameter to think about? I'd say that on any social network, I have meaningful, ongoing relationship with maybe 20 people. I suspect that's the norm. But that doesn't mean you can join a social network with 20 users and get that. I mean, if it's a mailing list for friends and family, sure. But not if it's 20 randomly-selected strangers from around the world.

So the critical mass to make the "random stranger" type of a social network work is much, much higher than the number of daily interactions you need to keep coming back.