The median home price jumped 18 percent to $825,000 in August from $700,000 a year earlier, according to DataQuick, a San Diego-based real-estate data provider. The median for existing condos soared to $810,000 from $630,000 in August 2010, while existing single-family detached homes rose to $870,000 from $688,000.

Housing Scarcity

“There’s nothing available, so housing prices go through the roof,” said Egan, the city’s economist. “There’s been a very robust amount of housing construction, but it has not yet had the effect of denting the growth in housing prices.”

Twitter in 2011 considered leaving San Francisco, telling Mayor Ed Lee in a meeting that a city tax based on the size of the company’s payroll would erode its growth. Months later, San Francisco had exempted Twitter from the payroll tax and made the same offer to other companies willing to relocate to Central Market, an area plagued by crime and empty storefronts within blocks of City Hall. Twitter moved into a renovated 1930s furniture mart there in June 2012.

Double Footprint

The company is in talks to lease a 320,000-square-foot office adjacent to its headquarters, according to people with knowledge of the discussions. That would more than double the company’s current footprint of 295,000 square feet, data from broker CBRE Group Inc. show.

Other companies have since followed Twitter’s example. Since April 2011, 15 technology companies have located in the Central Market area, including mobile-payment service Square Inc. and online retailer One Kings Lane Inc., according to Todd Rufo, director of the city’s Office of Economic and Workforce Development.

“They’ve single-handedly helped revive a depressed area of San Francisco by moving their headquarters to Mid-Market,” Kenneth Rosen, chairman of the Fisher Center for Real Estate and Urban Economics at the Haas School of Business at the University of California, Berkeley, said of Twitter.

“So the IPO will provide money for their corporate growth,” allowing them to add staff, Rosen said by telephone.

Affluent Influx