google+: Join some communities related to your website's topic, participate in them and then share your own content.
reddit: Take part in that community openly. Share anything useful, not only your site's data, and share your website's content only where it is the best possible available. reddit give a good number of visitors if you have quality content, unique and timely.
fb: Make a group or page or both for your website. Get your friends to like and follow you there. It will slowly attract more people, if you have quality content to offer, and hence some traffic in start. Facebook gives a huge amount of traffic, but it takes time.
Twitter: Stay active, share content, attract people to follow you with the power of your quality content, and there you go, visitors for your website.
StumbleUpon: It is also a good source for traffic. Share your content there and it send related traffic.
And more.
Interesting, quality, unique and timely content gets traffic from every social sites, what so ever.