The Tokyo company joined existing investors including Andreessen Horowitz, Bessemer Venture Partners, and FirstMark Capital, as well as unspecified angel investors, in a fundraising that reports suggest puts a $1.5 billion valuation on the whole of Pinterest.

Pinterest, whose CEO and co-founder is Ben Silbermann, allows users to share images, video and other content over the Internet and through mobile phones and build personalized scrap books.

As well as providing financing, Rakuten will help Pinterest expand in Japan and into Rakuten's 17 other markets.

"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 founder and CEO Hiroshi Mikitani in a statement. "We see tremendous synergies between Pinterest's vision and Rakuten's model for e-commerce."

The tie-up with Rakuten gives Pinterest a powerful springboard for expansion.

The 15-year-old Tokyo company has a market value of ¥1.12 trillion ($14 billion) and its tentacles extend across Asia Pacific, the Americas and Europe.

Rakuten's U.S. acquisitions having included Buy.com, an Aliso Viejo, Calif. online shopping site, and LinkShare Corp., a New York marketing services provider.

In January Rakuten took on titan Amazon.com Inc.'s top-selling Kindle with its purchase of Toronto e-reader maker Kobo Inc.

Mikitani told the Financial Times he would have been willing to invest the entire $100 million without the co-investors.