Hi,
The plugin displays "like" buttons on the product pages so that the customers can click on them in order to share the product on their facebook/google+/twitter/pinterest wall/feed.
It helps in the promotion of the products, but only if people share the products on their wall/feed by clicking on the like buttons.
Having the plugin enabled doesn't promote the products on social media per se.
That's why we didn't add these buttons on our products on our website as we don't see why people would share our products on their social networks with their friends as our products are for business use.
A more effective way of promoting products, is to have quality content on your website. For example, you could have a blog with valuable information that could interest the people interested in buying your products and then share these articles on social media. That's way more effective, and even could increase your page rank on search results in the long run.
It's actually something we should do too on our website, if only we had more time to focus on marketing... Giving tips and tricks on building great online shops would surely interest many users and increase our promotion via social networks.
From what I understand, that's what any SEO expert will tell you: rather than focus on the details of your website SEO, it's better to use that time to create great content.