Zillow, the Seattle online real estate company, today posted a 73 percent increase in fourth quarter revenue as the number of Premier Agent subscribers grew by 2,770. It now has 29,473 agents in the program, up 87 percent year-over-year.

Zillow — which acquired three companies in the fourth quarter to bolster its offerings in rentals and mortgages — showed revenue of $34.3 million for the quarter. Net income came in at $549,000 — down from $922,000 for the same period in 2011.

Zillow finished the quarter with $150 million in cash and cash equivalents. It now employs more than 600 people. In an interview with GeekWire, CEO Spencer Rascoff called it a “terrific quarter” that capped a record year.

“Mobile continues to be a huge accelerant to the business,” said Rascoff. “In the quarter, we had more homes viewed on mobile than on desktop, and we had more visits on mobile than on desktop. And Zillow monetizes incredibly well on mobile.”

Spencer Rascoff of Zillow

He said that home shoppers browsing Zillow on mobile are three times as likely to contact an agent than on the desktop.

The stock is soaring on the earnings news, up more than 13 percent in after hours trading at about $44 per share. The stock had already climbed seven percent in regular trading today, and now boasts a market value of $1.3 billion. The stock is up 40 percent so far this year, and is now trading at more than double its July 2011 IPO price.

The stock is up, largely because Zillow beat analysts’ expectations by a wide margin, doubling expectations of EBITDA during the quarter (coming in at $6.8 million) and beating revenue estimates by about $3 million. Rascoff called the sales teams’ performance during the quarter “superb,” with full year revenue coming in at about $117 million.

The positive earnings report comes as Zillow heads into its busiest time period when Americans increasingly look to buy and sell homes. Because of that, Rascoff said that traffic is soaring, up 45 percent in January to more than 45 million unique visitors.

Rascoff said that the company plans to “step on the gas” when it comes to advertising, boosting that spend by more than 70 percent in 2013. “There’s a huge brand white space in this category,” he said. Zillow last week announced that it plans to roll out a nationwide TV campaign on HGTV, Comedy Central and other channels.

Zillow expects revenue of $165 million to $170 million in 2013.

Shares of Zillow rival, Trulia, also are up today after the San Francisco company reported a 75 percent increase in fourth quarter revenue. It posted quarterly revenue of $20.6 million, and a pro forma net loss of $800,000. It posted 23.6 million in monthly visitors.

Here’s the full Zillow earnings release:

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