Mayor Edwin M. Lee announced salesforce.com has leased approximately 450,000 square feet of office space in a new office tower to be built at 350 Mission Street. The largest San Francisco lease transaction of 2012 to date, the building will break ground in January 2013 with anticipated occupancy in 2015. Salesforce.com also announced a 100,000 square foot expansion at 50 Fremont Street. This comes less than a year after salesforce.com’s January 2012 announcement of a 400,000 square foot lease in the same building.

“Salesforce.com’s major expansion downtown proves once again that investor confidence is driving San Francisco’s economic recovery,” said Mayor Lee. “This will bring thousands of new jobs and anchor the City’s Transbay District as a leading destination for innovative companies. Salesforce.com started in San Francisco, and I want to thank Marc Benioff and salesforce.com for their commitment to grow and add jobs in the City.”

“I’d like to thank Mayor Lee and his team for their continued support of Salesforce.com’s expanding downtown San Francisco campus,” said salesforce.com COO George Hu. “We are proud to have our global headquarters in San Francisco and are committed to continuing to grow and add jobs in the City.”

Owned by Kilroy Realty, the 27-story office building at 350 Mission is set to break ground in January 2013 becoming the first new high-rise building built in San Francisco since 2008 and will be the first new LEED Platinum office tower in San Francisco.

“Eight weeks from purchase to full pre-lease is a new record for Kilroy Realty Corporation” said Kilroy Realty CEO John Kilroy. “It’s an incredible outcome that couldn’t have been achieved without a phenomenal tenant in salesforce.com and the support of the Mayor’s office. We are so thrilled to have salesforce.com occupy this iconic tower in the heart of the South Financial District.”

50 Fremont Street is owned by TIAA-CREF.

Today’s announced leases total more than half a million square feet and will provide space for thousands of new employees in San Francisco. This move expands salesforce.com’s “downtown campus” and is adjacent to the new Transbay Terminal under construction. Salesforce.com will have 1.6 million square feet of office space in San Francisco by 2016, reinforcing their status as one of the City’s largest employers.