Word of Mouth Marketing
Marketing through word of mouth, referrals from happy customers, for example, has long been a most effective technique for many businesses. People are more likely to be convinced by someone who has had a positive experience with a company than by an impersonal image on TV.
The past few years have seen a growth in social media and, what is more important, a change in the demographics of the users of social media. Research now shows that over 35-year-olds now form a major component of social media users. Something like Twitter is a means of reaching out in a word of mouth fashion. Re-tweets can extend the message to a wider audience. Media like Twitter, Facebook, Linkedin, Flickr, Digg, etc all offer the opportunity to advertise by word of mouth. It's the new way and many companies are picking up on it. A good article on this topic is found in E-Commerce News.