Everyone who tweets would love to boast huge numbers of Twitter followers. There are some services that sell Twitter followers, and all you, the tweeter, have to do is sit back and enjoy the thrill of being followed and imagining that your followers are hanging onto your every word -- which, obviously, will largely revolve around your book publicity campaign. So you're probably thinking that it would be a brilliant book publicity strategy to buy a massive number of Twitter followers and enjoy the fruits of your tweeting efforts.
I'm sorry to be the one to break the news to you, but I've just read an MSNBC article that cautions against trusting the purveyors of Twitter marketing lists. You might want to read the article yourself before you sign on the dotted line with any company that can instantly add thousands of followers to your Twitter account. According to the article, so-called bulk following services (which are sometimes free) can actually cause your genuine followers to "unfollow" you because, in their user's agreements, the services obtain the right to use your Twitter account to send out their own self-promotional tweets which can be either annoying or outright offensive.
So it seems that there's no shortcut to gaining Twitter followers. If you're using Twitter as part of your book publicity campaign, you have to win your Twitter followers the old-fashioned way -- through hard work and promotion, promotion, promotion!
