It will probably count as 1 backlink as all the links will be on one site, ie twitter.com. Therefore, I doubt it will help SEO much. However, it does drive traffic to your site if you have a lot of followers or retweets.
Twitter has so many outgoing links that their No-Follow backlinks basically don't register (just like posting on Facebook, LinkedIn, or any other popular social media).
But as mentioned above, Twitter is a great way to drive traffic. More traffic means Google will see your site as more relevant, and thus move you up in the search engines.
Twitter is the most talked about social media website when it comes to the second screen. Any time there is a major awards show or sporting events the blue Twitter bird and hashtag symbol are on the TV screen every 15 seconds. It is remarkable how embedded Twitter now is when it comes to watching TV and looking at a smartphone or tablet. Unfortunately, the lifespan of a tweet is about 30 seconds, if that. With a tweet having 30 seconds of fame one would hope it could help a website in terms of search ranking. That is simply not the case. At this point, most tweets are not indexed by Google and the links do not help with SEO.
Twitter doesn't provide backlinks, all are no-follow links, so those links not helpfull for direct ranking in search engine, but maybe it's positive effecting in ranking.. I am not sure but social single may helpful for ranking..