Out of 100 million users, there might be a couple thousand users who are worth following, and out of those couple thousand worth-following users, only a couple hundred might share the activities that you are interested in.
So far the only option was to browse for users based on a optic, or search a 3rd party twitter directory.
Twitter just announced a new feature, “Suggestions for you,” that will help users follow people who are more relevant to their network, interests, etc..
The new tab is added to “Find People” page on your twitter account. Simply click on “Suggestion For You” and you will see the list of people who you might be interested in following. These suggestions are based on people who you following and people who are followed by people you follow.
Click here to try it out.