Zillow is making a big bet on its operations in southern California, announcing today that it plans to open a new office in Irvine with room for 100 employees. The announcement follows last year’s acquisition of Diverse Solutions, which is based in Irvine. Diverse Solutions’ 19 employees will move to the new facility, which is expected to open later this summer.

Most of the new hires at Zillow’s Orange County operations will occur in sales, selling premier agent subscriptions and advertising as part of the Yahoo-Zillow Real Estate Network. Zillow announced a renewal of the advertising agreement with Yahoo earlier this month.

“As Zillow continues to expand the breadth of our services and develop new tools to help real estate professionals grow their business, it made perfect sense to also expand our sales force to Southern California,” said Greg Schwartz, Zillow’s chief revenue officer. “Orange County is part of America’s largest real estate market and has created a deep pool of talented sales people with expertise in Internet marketing and software from which to recruit.”

Zillow moved into a new 66,000 square-foot headquarters in downtown Seattle last year, and we’ve heard that they are already looking for more space to keep up with growth.

“We’ve nearly doubled headcount in the last year so, if we keep growing at this pace, we’ll eventually need more space,” said company spokeswoman Cynthia Nowak.

Shares of Zillow have been on an absolute rocketship ride in recent weeks, but they took a nosedive today as the stock fell nearly six percent to $34.82. Zillow, which is profitable and had revenue of $20 million during the fourth quarter, now boasts a market value of $993 million.

News also came out today that Zillow’s primary rival, San Francisco’s Trulia, has chosen JPMorgan Chase & Co.  and Deutsche Bank AG to manage an initial public offering. Trulia attracts more than 20 million users per month, while Zillow reported 32 million unique visitors to its Web site and mobile apps last month.

Zillow now employs close to 400 people, with the majority in Seattle.

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