There are plenty of websites with valuable content but too few comments. Sometimes you just have to give your visitors and readers a nudge to encourage them to comment more. Comments Leaderboard for WP can help. It lets you track top commenters on your site and gamifies the process.
This plugin simply encourages people to contribute more to your site with their comments. Commenters have a better chance to get their name and link more exposure as they climb the comments leaderboard. The overall leader gets a medal next to her name and maximum amount of visibility.
Your readers will be able to see the number of comments posted by each user, so they know how much effort they have to put forth to climb the rankings. This is a free plugin.