[Air-L] Locating passive consumers on social network sites

Hi everyone, I’m doing a project that focuses on how people consume and respond to political content on a Twitter-like social network site. I was planning to target both active people who are highly interested in these contents, showing by posting comments (I actually found this group of people via reading the comments they posted on) or re-sending them; and passive consumers, who basically only read these contents. The problem is, it is hard to reach these passive population on a social network site. Does anyone have tips on locating these people or any literature about this question? Many thanks. Mengyao Yuan PhD student of sociology University of Edinburgh Email: maya.yuan2010@gmail.com