Twitter have a whole department to deal with spam. I have no idea why they need it as a spam does not seem to get very far on Twitter and I have no idea why a spammer would even want to use it for spam. I used to see some spam a while back, mostly Amazon.com affiliate links, but lately there has not been any that I have seen.
How do you use Twitter? Who do you follow? You should only be following those that tweet the kind of information that you want in your daily life or your work. What is the point in following a whole lot of other who do not post useful information? Why would you follow someone that spams? There is nothing in it for spammers, though they try.
Some places, like over at Fiverr, will try and sell you a service to get you a 1000 or so followers that you can tweet to. But who are they; they are all fake accounts and do not have the slightest interest in the information that you are tweeting, so why bother? There are plenty of ways to try and make money from Twitter; but there are even better ways to get timely information to act on!
Twitter is great. Use it for what it is intended for. Tweet what your followers want to read about. Follow those who tweet what you want to read about. Cut loose all the others.