Ask HN: How to beat the chicken egg situation with user-content driven website?

We’re working on capitalizing on craigslist’s weaknesses, and while we have a good grasp on what we’re doing; we aren’t sure how to attract users to a fresh classifieds website. Users tend to leave when they see a website without much there, and obviously new ads won’t list themselves. How can we go about creating real incentive for sticking around when there are still not many listings?