There was a lot of discussion on this a while back. See: What would it take to replace Facebook with Discourse?, Community has no boundary: Discourse-as-a-Fabric - ideation & brainstorm and to some extent Facebook Groups - Zuck is coming for us
Personally I think Discourse is designed for small to medium-sized discrete instances, not MASSIVE scale. However many suitable plugins (like our Follow plugin) exist to close the gap.
You can do this with our Topic List Previews plugin which amongst other things, adds a Like button to each entry on the Topic List.