There is a website called TweetBig that you can try for free for one month. I went from 7 followers to 1500 during that month, and several months later still have about 7 new followers a day. I should have kept using it because you can also set up tweets on a timer to send traffic to your hubs. Doing this tripled the traffic to my hubs. I was going to write a hub about TweetBig but never got around to it.