Retweets, 'Likes', +1's and the rest of them are great for brand recognition, but not so much for SEO. If you combine solid SEO tactics with great social media activity, you should find yourself at the top of the rankings in no time. Google wants to tell you that the social media stats may not be important, but as more and more of our marketing efforts move to these channels, they will start being incredibly important. That said, DON'T EVER BUY LIKES, RETWEETS, OR +1'S. Not cool, bro. Not cool.
Retweets helps you build authority. If a lot of people are interested in what you say and retweets you, google will see you as an authority. You will rank better. Thats whay social media presence is so important today.
It seems that website mentions are getting more and more importance in rankings. Don't look at tweets as much as links but as website mentions to get some SEO benefits
Yes, Retweets are useful in SEO indirectly. It acts as a social signal for search engines like Bing and Google.