Call it the Facebook effect in the wake of the largest hi-tech IPO offering.  Pinterest is the lastest to enter the exclusive club of companies valued at $1 billion dollars thanks to the recent investment led by Rakuten. The social network has raised $100 million from Japanese e-commerce giant Rakuten along with Andreessen Horowitz, Bessemer Venture Partners and FirstMark Capital along with angel investment, putting the startup’s value at $1.5 billion.

Rakuten said that this investment helps the site grow in the U.S. and its 17 overseas markets, including entry into Japanese market.

“While some may see e-commerce as a straightforward vending machine-like experience, we believe it is a living process where both retailers and consumers can communicate, discover, and curate to make the experience more entertaining,” said Rakuten CEO Hiroshi Mikitani. “We see tremendous synergies between Pinterest’s vision and Rakuten’s model for e-commerce. Rakuten looks forward to introducing Pinterest to the Japanese market as well as other markets around the world.”

Pinterest has become the sensation of recent social media history, and has positioned itself as the third largest social network in the US.  Pinterest, where users can share their photos, has grown rapidly in recent months–the website has become the sixteenth most visited site in the US, according to Alexa.  In April alone their user base has reached more than 20 million, up from 1 million in July 2011.

“Our goal is to help people discover things they love, by connecting people through their shared interests. Bringing Rakuten on board gives us an amazing opportunity to move a step closer to this goal,” said Pinterest CEO Ben Silberman.

A partnership with Rakuten could open many doors for Pinterest to expand its presence in Asia. The company sees great potential in markets like France, Germany, Japan, Portugal and Spain.

Pinterest Weekly – New Platform to Keep Users Engaged

Pinterest remains undefined in its business model, at least publicly, and the company has yet to disclose its revenue.  But faced with such high expectations and an outstanding valuation, it’s time for Pinterest to start developing its user engagement and monetization strategies.

One step in that direction is the introduction of Pinterest Weekly, a weekly email board. The company has started sending users a weekly e-mail featuring basic account stats, like their top pins, and other popular boards in an attempt to keep them engaged between pinning sessions. This week’s feature is user George Takei’s “Cats and Dogs” as he shares “Pins You Might Like” from users’ friends.

Pinterest as a social network is more popular amongst the ladies, and has been nicknamed the “Tumblr for girls” as women trust product recommendations reviews from this social networking site. Amazon recently integrated Pinterest to their service in an attempt to drive more consumers to their retail outlet, particularly including women, and power more recommendations.