Finding followers on Twitter is one thing. Finding the right followers is an other matter, however.
From a business point of view, you want followers that are potentially interested in what you have to offer them. This means you have to go through a selection process, searching for people to follow in the hope they'll follow you back. This goes through:
- An efficient and appealing bio and profile. Most people receive an e-mail when someone follows them (because they didn't disable this function which is on by default), that e-mail contains your bio and a link to your profile. You must get them interested at that point.
- Keyword searches: you can find people to follow by using a keyword search, but also by using search parameters in order to refine your query. Learn more about this in this tutorial: Twitter tutorials, stage 5: find people to follow manually
- Automation tools: there are some tools out there, online services or applications you can install on your computer, that will allow you to automate your Twitter tasks. TweetAttacks is probably the best tool for this, but it is also quite complex and some good training might be in order if you want to do this seriously. Update: TweetAttacks is no more. If you have it, it will keep working for the time being and you may still be interested in the training, but if you don't have it, you can't buy it anymore. I will soon replace it here with another tool, probably the one I actually use every day (I wasn't using TweetAttacks because it's a windows-only tool).
- The right behavior: finding followers shouldn't be your only concern, keeping them is also something you should think about. Offer them content and information they'll be interested in, don't send them only directly business-related tweets (promotional offers and stuff to buy).
One thing you shouldn't do however, is buying Twitter followers. You'll find offers out there for this, but these are people who are not interested at all in what you have to offer, in other words they are worthless and there's no guarantee they won't stop following you after some time.