You need to register an account with Klout in order to use it, but this is an easy step which takes about 1 minute. Once you've created an account on Klout, you can log in and search for your desired topic in the search bar at the top of the screen. This will bring up a list of the top 9 influencers for that topic. These influencers are calculated according to who has generated the most engaging content on your topic in the last 90 days. If you click on a specific influencer, you will see links to all their social media and blogging profiles. The tool is free to use.