I’ve just started to use Twollow.com it’s a neat Twitter app. that allows you to auto follow people who mention keywords that you are interested in. If you want to build a community of interest around a certain word, theme or meme then enter the keyword on the site and it will track all Tweets that mention it. You will then auto follow the person who mentioned it.
Beware of using words that are too general otherwise your follower count will go through the roof and Twitter is likely to ban you as a potential spammer. However it’s a useful tool for brand owners who want to build followers who are talking about their company or product.