Twitter Helps Revive a Seedy San Francisco Neighborhood Peter DaSilva for The New York Times Twitter's San Francisco headquarters, in a 1937 Art Deco building. Many tech industry firms are expanding to the city. SAN FRANCISCO - The middle stretch of Market Street here has befuddled mayors, investors and entrepreneurs for decades. The 37-story Crescent Heights apartment tower in San Francisco. Apartments are to be tailored to tech industry workers. Studded with check-cashing joints, strip clubs and dollar stores, the seven-block strip known as the Mid-Market had resisted cleanup efforts and resolutely remained the same: a seedy place to visit day or night. Even the area's community groups said they were fearful. Mid-Market is home to some of the highest vacancy rates in the city for office or retail, despite its proximity to City Hall, which is a few blocks away. So it seemed implausible that a young company, heralded as one of the technology industry's next big things, would want to make its headquarters in Mid-Market. But in April 2011, that young company, Twitter, dispelled rumors that it was leaving San Francisco for a nearby city suburb and instead announced it was relocating to Mid-Market. In June 2012, it moved in. Twitter leased space from Shorenstein Properties, a real estate firm based in San Francisco, known for its blue-chip office towers in the Financial District here. Shorenstein bought an 11-story building in 2011 fronting Mid-Market that had been vacant for five years. For them, it made sense to buy the undervalued Art Deco landmark built in 1937, which had some of the most spacious floor plans in the city at a time when office space was tight. Twitter signed a lease until 2021 for 295,000 square feet in the building and could expand that as its work force grows. In our gut, we believed if we changed it, they would come. We thought it would be a real catalyst for the neighborhood," said Charles W. Malet, chief investment officer for Shorenstein Properties. Now 15 other companies, like Spotify, Square and Yammer, emboldened by Twitter's move and a city tax incentive that largely exempts them from city payroll taxes if they relocate to the Mid-Market, have committed to take 1.3 million square feet in the area, which the city has renamed Central Market. Apartment towers with 5,500 units are in the works, and arts groups, chefs, retailers and even a venture capital firm have taken up residence. "You had a once vacant and blighted area that is now a gravitational center for some of the most innovative companies in the world," said Todd Rufo, director of the San Francisco Office of Economic and Workforce Development. Not to be outdone, the rest of San Francisco is in the middle of an impressive building boom. Developers are building office towers downtown for the first time in five years, many confident enough to build without signed leases for the space. Other buildings are undergoing extensive renovation. Branches of technology companies, old and new, like Google, Amazon, Microsoft and Yahoo, are expanding or moving to the city and now make up more than half of demand for office space. During the tech bubble in the late 1990s, tech accounted for only a quarter of demand. "People tend to build when they can lease and make money," said Meade N. Boutwell, a senior vice president at commercial real estate brokerage C.B.R.E. in San Francisco. In 2013, San Francisco became the second-most-expensive city in the country, behind New York, in which to rent office space. Rents rose from to $53.84 per square foot from $46.12 in the third quarter, according to C.B.R.E. Vacancy levels stand at 8.2 percent, down from 9.7 percent the same time last year. Four years ago, it was 15 percent. Rob Speyer, co-chief executive officer of Tishman Speyer, a big real estate developer based in New York, said, "San Francisco has led the U.S. commercial real estate market out of the financial crisis." Tishman Speyer is betting heavily on the city by starting construction on two speculative office buildings with debt-free financing. After buying a parking lot in an area called South of Market, or SoMa, the firm began building the city's first speculative office tower since the recession. Nearly 18 months into construction, Neustar, a data analytics company, agreed to lease four of the building's 10 floors to consolidate its Bay Area offices. "This is a strategic decision for 10 years, not three," said Mark F. Bregman, Neustar's senior vice president and chief technology officer.