Finding those on social media who have influence has always been a challenge, but a crucial one to master.
How else are you going to focus your efforts on those who matter for your campaign, issue or company? The Tools I use to do this are:
Visualize Twitter communities and find who is influential in them
Finding the right hashtag to use to get your Tweets seen.
Analysis of your Twitter followers, who are they, what are they talking about and when is the best time to post.