Social networks or social networking sites are a great way to get your products or services in front of millions of people. Almost all social networking sites allow you to create a free profile that can be seen by other people. That profile can be used to "direct" the traffic to either the main site or sales pages.
To be successful with using social networking sites you have interact with the network and establish relationships with other network members. Otherwise, you can be seen as a spammer and even if your profile will not get deleted, you will not make any money using the social sites.