NEW YORK (TheStreet) -- Zillow (Z) - Get Report  was plunging after regular market trading on Wednesday as the online real estate marketplace offered revenue forecasts for the current quarter that fell short of analyst expectations. Investors took issue with the slowing growth of display advertising, which Zillow said is likely to continue into the fourth quarter.

Seattle-based Zillow forecast revenue for the fourth-quarter as high as $90 million, short of the $91 million projected by sell-side analysts surveyed by Bloomberg. The company said full-year revenue is expected to fall within the range of $322.5 million to $323.5 million, also short of analysts' estimate of $324.1 million.

Shares were tumbling 9.4% in after-market trading after closing at $103.77, a 27% advance for 2014. 

Zillow reported a gain of an adjusted 13 cents a share on $88.6 million in revenue, up 66% year over year. Zillow's Marketplace segment, which includes the company's real estate and mortgages segments, jumped 77% year over year to $72.7 million. Display revenue, otherwise known as advertising, grew 30% to $16 million. Analysts surveyed by Thomson Reuters were expecting an adjusted gain of 8 cents on $88 million in revenue. 

On a GAAP basis, Zillow lost 40 cents a share with results negatively impacted by costs associated with its pending purchase of online real-estate rival Trulia. CEO Spencer Rascoff told TheStreet Wednesday afternoon he expects the all-stock deal for Trulia to close in the first half of 2015. The deal is currently under review by the Federal Trade Commission.

Zillow added 4,059 Premier Agent advertisers during the quarter, bringing the total to 60,877, as average revenue per agent (ARPA) reached $349, up from $320 in the second quarter.

"This is the sixteenth quarter in a row of 65% plus year-over-year revenue growth, which is nearly unprecedented sustained hyper revenue growth," he said during a phone interview with TheStreet. "I still feel like it's very early days for us relative to the opportunity. ... Over a multi-year period [real-estate] agent advertising budgets are migrating, and will migrate, to where the audience is."

Rascoff's point being that Zillow's top ad buyers will follow prospective home buyers to web and mobile. Zillow saw 89 million unique visitors on its mobile and web properties in July 2014, as the housing market continues to rebound, and buyers are searching for homes on Zillow properties. Visits to Zillow via a mobile device in the quarter grew 70% over the same period one year ago. In September, 500 million homes were viewed on Zillow from a mobile device.

Zillow shares finished the regular session down 3.53% to close at $103.77.

--Written by Jennifer van Grove in San Diego, Calif.

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