Once your business catches attention, it would automatically turn it to good business. Here the investment of money is there, but it would be worth it, rather than spending on the traditional earlier ways of advertising, as you don't get a global perform there. The social media network gives you r business a global coverage and that way you reach a greater audience to fix your target.
In case of facebook, you have make interesting page posts. And using that you can get some traffic on the website. It takes a lot of time to build the traffic from facebook. So make sure that you have some dedicated time and money to spend for the same.
In case of twitter, your message has to be short and attractive. This way you can use it for sending the traffic. The traffic is not that good but definitely worth investing if you have product or service.
Other social networks such as linkedin, diaspora, google plus are only worth it if you are just randomly sharing content. otherwise don't expect much from the social networks.