Growing an audience with high-quality but infrequently updated content on a diverse set of topics

I write a data journalism blog called The 10 and 3. Our goal is to tell interesting, quirky and fun stories about Canada using charts, maps and other interactive data visualization techniques.

We have produced about 15 pieces of (very) high-quality content and most it has been quite well-received. In fact, some of our posts have been read over 50 K times.

Our challenge is that every time we create a new post, we have to basically start from scratch in terms of finding our audience. We have under 200 followers on Twitter and Facebook and an email list of only around 100 addresses so our reach is not significant. It has been tough to grow this audience because our posts are on a broad range of topics and many people who are in love with a specific post may not find the rest of our posts that interesting.

I would appreciate any industry-specific (news/journalism) advice we can use to help grow our audience, specifically on Twitter and Facebook. As of now, we use Reddit and a few connections we have made with journalists to find audiences that will like our individual posts but it is a very unidimensional approach and we want to approach this challenge in a more multi-dimensional manner. Any advice would be greatly appreciated.