Several methods have worked with different people but as a caution, you must remove the idea of buying because most times its always full of bots and for the bounty that are serious, Twitter audit tool can do justice by exposing the number of fake followers which bring you back to where you started from.

For me, I had initially struggled with building followers but taking it by the head is opening a new one with crypto related name. This for one gave the purpose of what its about on first look. There after, I changed the wordings to crypto related ones such as #btc, #bitcoin, #ico etc and most importantly is 'follow back' in addition to using a twitter tool that sends message to anyone that follows me by appreciating them and encouraging them to be patient as I will follow back.

With the above, I then limit the people I follow to those who have it on their own platform that they will also follow back and that has proven to be a working solution. It takes perseverance but slow and steady, you can get there.