Ask HN: How do I expand my worldview and meet smart people online?

Going to a big school and meeting people with different backgrounds and interests has made me painfully aware of how ignorant I am. I'd like to meet people who will challenge me intellectually and act as a catalyst for my growth. I'm thinking of reading some lesswrong posts and hanging around in the comments and perhaps exploring that part of the internet. It's not perfect but it's a start I guess. What are some of your experiences with meeting people on the internet and how does one go about meeting great people?