Pinterest — a relatively new social network/online service which allows users to create "pinboards" for pinning links, images and Web pages, among other things — is the fastest growing social media traffic source for e-commerce websites in term of revenue, according to Jeffrey Zwelling, CEO of marketing company Converto.

Zwelling — whose company tracks marketing performance across a number of channels including Facebook, Twitter (News - Alert), Pinterest and others — contends that Pinterest's percentage of all accumulated social media revenue for e-commerce sites grew to 17.4 percent as compared to 1.2 percent in the second quarter of 2011. Zwelling also projects that Pinterest will be responsible for about 40 percent of social media e-commerce transactions by the end of the second quarter of 2012, cutting into Facebook's (News - Alert) share and reducing it to just under 60 percent as compared to 86 percent from a year ago.

Part of the reason for this, suggests Zwelling, is because Pinterest tends to introduce new customers to client's websites, making it an invaluable marketing source. This tendency to introduce customers to new retailers is far more valuable than reinforcing users' already established interests as is more commonly the case with Facebook. Furthermore, it seems that, by Converto's estimates, Pinterest generates more revenue per ad clicked than Facebook at 45 cents per click to 40.

Perhaps this threat to Facebook's social media e-commerce transactions market share is part of the reason for the company's recent acquisition of popular mobile image sharing app, Instagram, for the sum of $1 billion.

Pinterest — which is commonly used to plan weddings, organize recipes and show off new fashions — claimed recently that its main interest is not on monetizing, however, claiming that its focus is on customers first. This statement came shortly after the company stopped using Skimlinks, an e-commerce company which claims to use "unintrusive" methods to help companies make money, after Pinterest users discovered that the service was being used and expressed dislike for its subtle methods.