Tweeting hashtags won't do almost anything. Also buying twitter followers is only good for one reason, when you have 8000 followers you can follow ~9000 people.
I'll show you how to grow it fast:
1. Pick a popular niche (Cute animal pictures, Tattoos, whatever)
2. Go to a popular account in that niche, and use imacros to follow 900 people.
3. Post a couple pictures/tweets a day, steal them from other accounts probably
4. Repeat step 2 for 10 days, then unfollow all of them 1000-2000 people a day.
In a month you'll have a lot of real followers, and you'll be able to grow just from other people. You could also get banned, but twitters pretty damn lenient, I've unfollowed 3300 people in a single day and not got banned