My startup just launched a blog, and I am trying to build an audience. What distribution tactics will be effective?
Some great suggestions here already! In addition to guest posting, I'd recommend optimizing your posts for SEO. If you're consistent, this will really pay off over time, and you'll get far more bang from your archives as they catch on in search.
Even if you're not an SEO guru, you can take simple steps to improve your SEO. The easiest one is using keywords in your headlines. Lots of other simple ideas in this free webinar: http://alexisgrant.com/webinar-seo/
For some of the blogs we manage, we've also established syndication partners -- big outlets like AOL and Business Insider that want our content and send traffic to us in return. That's something to consider once you've gotten in the habit of providing awesome content.