ZillowLogoDecember yielded incredible results for property search upstart Zillow.com.

They proudly reported that their property engine is hitting on all cylinders. On the traffic front, they saw a burst of traffic. Thanks in part to their partnership with Yahoo! and hundreds of local newspapers, 13 million consumers visited their website during the month of December. These are not only huge numbers, but they represent an impressive 77% growth over last year.

For a venture-funded start up, they are on the right track. Along those lines, like their cross-town industry rival Trulia, Zillow posted a profit in 2010. They have officially crossed the revenue chasm and do not seem to have much in their path for continued profitability and growth.

Key to their profit success has been advertising and the Mortgage Marketplace. 13 Million consumers generate a lot of banner advertising and they are always offering new advertising units to agents and brokers. Moreover, Zillow Mortgage Marketplace is just shy of generating 300,000 consumer loan requests per month.

Clearly they are on the right track at combining mortgage and listing content on their site. Realtor.com launched a mortgage component to their site last month to capitalize on the opportunity too. On another note Zillow did announce that they passed the 100 million homes on Zillow mark which is a combination of active and sold property records.