"Tech guys want open ceilings with all the exposed wires and pipes," according to David Phu, director of information services at TRI Real Estate.

Some of the young Internet firms can locate in San Francisco because they don't need big industrial spaces, said Colin Yasukochi, director of research and analysis at the commercial real estate firm CBRE. And outsourcing means some companies require less space for engineering staff.

Pinterest's new headquarters are just around the corner from Zynga. Dropbox, which offers cloud storage, opened its doors in April five blocks away. Home vacation rentals provider Airbnb will next year into a cavernous building down the block from Zynga that now houses a Diamond Exchange.

Yammer, which was recently by Microsoft, leased a spot nearby in early 2011.

Klout, a social-networking status ranking service that launched in 2011, set up shop specifically to be close to Twitter, said Lynn Fox, a spokeswoman. Twitter founder Jack Dorsey's latest project, Square, has its offices in the Yelp, which went public earlier this year, already has its offices in SoMa, but will move next year into a larger space in the same area.