Chapter 4 of the Briggs text is about microblogging, and especially Twitter. Read the Pew Research Internet Project’s Social Media Update 2014 to get a broader sense of who’s on social media and which platforms they prefer.
As much as journalists use Twitter (which is a lot), it’s not the best way to reach some audiences. Read A Teenager’s View on Social Media Part 1 and Part 2, written by a University of Texas student. What do you think, does he nail it? Or is your experience different?