Conversations on the topic of list building seem to lack nuance with a tendency to focus on which media is performing best. The thing is, your first question should be, how your niche is distributed in 5 different audiences based on your current relationship.

Are you targeting cold traffic who have no idea who you are or warm traffic who have previous knowledge of who you are and some level of trust?

WIDEN THE NET USING CONTENT - COLD TRAFFIC

• Cold Audience 1: Friends of Friends
  
  Some of the people in your niche won’t know you at all. When they see your name for the first time, they will have no idea about who you are or what you can do for them. But there is an opportunity to engage those who already know you in activities that are broadcasted in the news feeds of their friends on social media. Who would you listen to more? Someone you never heard of or someone your friend listens to?
  
  Activate and engage your followers in activities RELEVANT to your business...