I have only met a few people IRL via HN, but have definitely built my network through it. That is to say I've built connection with people that I either met on HN and then connect with elsewhere online, or met them in real life. In one case I interacted with someone on HN, then helped them get a job, and then later they wrote something for my company, then we have interacted several times on LinkedIn.
Maybe I misread your comment, but I don't think that meeting someone in person is required to build a network.
Maybe I misread your comment, but I don't think that meeting someone in person is required to build a network.