I maintain an email networking group over at CTOLunches.com, and email is the only channel I allow. Several people have asked about Slack, but email is the tried & true async medium that won't be going away ever.
For a social network, I see it being a cross between a Google Group and a newsletter.
* List my profile somewhere with a sign up box to "subscribe to updates and conversation from Miles and his network." * Every 3-6 weeks, I receive an email from the platform asking me what's been up with me, and I simply reply, which then gets sent to people who subscribed from updates from me. * Calendar integration -- when I add an event to my calendar, I have the option of including it in my next update to my email network to let them know I'm doing it. (ex: I'm speaking next month at some conference) * Community participation -- if anyone who subscribes to my email updates/network wants to email my network (ex: do you know anyone who...), I get an email saying my subscriber Bob wants to ask my network a connection, would you like to include it in your next email update to your network? If I respond yes, then it is also listed in my next email update to my network.
Something like that would be awesome.