The most active users or participants in a given community are often called opinion leaders. Often, the number of mentions (comments associated with a specific topic/brand/product/theme), defines the rank. An opinion leader is a person who influences others, knows the given topic well, produces good quality content, is authentic, and last but not least, can influence a sizable portion of a target group.
When measuring social media, clients do not always decide in advance how they will address individuals (i.e. blogger, forum, Twitter, or Facebook users), and how these people can be “utilized”. Often, the goal is to involve these participants in the viral spreading marketing communications. But they could also be recruited to help with product or service testing, or as research participants.
When choosing opinion leaders, the purpose should first be defined with an appropriate mechanism set up to achieve that goal, along with a valuation system to measure relevancy, reach, content quality, authenticity and activity. Also, one may want to focus on the opinion leader of a particular brand, or the opinion leader of other topics of interest to consumers.