Both Reddit and HN were seeded by people who read your essays (I was there for both).
How would you have advised "The Muffins" to overcome the chicken and egg problem without the assistance of your audience and YC's press attention?
I know they simulated user activity using fake accounts to overcome the "ghost town" effect. How could they have attracted the first critical few thousand users without leveraging an existing audience?
From your office hours talk I suspect you may suggest finding an especially enthusiastic niche audience at first. Certainly Reddit was all startup/hackers.
The problem is: how do you actually go about getting that targeted audience on the site in big enough numbers to jump-start the virtuous cycle?
(I'm really curious to hear PG's answer, but also love input from others as well.)
Borrow someone else's existing audience.
There are a couple ways to do this. The most straightforward is literally asking them for it. Somewhat surprisingly, people do say "yes" to this. (Joel Spolsky had a subreddit back in the early days, to share links with his fans. </trivia>)
There are various flavors of this in many services. Lady Gaga says all good little monsters follow her on Twitter, etc.
There are, of course, less savory options. The go-to option for many people is spamming Craigslist.