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What's happening? 
Shares of online real estate specialist Zillow Inc (NASDAQ:ZG) jumped as much as 13% early Friday after it announced Zillow Pro for Brokers has exceeded 5,000 partners.

Why it's happening 
Make no mistake: Zillow Pro for Brokers exceeding the 5,000-partner mark just three weeks into 2015 is extremely impressive.

First, Zillow Pro for Brokers has more than doubled in size since its launch in June, 2012. For perspective on its accelerating growth, note that when Zillow added Re/Max Select Realty to its partners this past November, it stated "Currently more than 2,000 partners across the country participate in Zillow Pro for Brokers." Then last month, Zillow announced it had added approximately 3,800 new brokers to the program when all was said and done in 2014.

It also helps that Zillow effectively doubled down on its support for real estate pros earlier this month by forming a dedicated team to serve their unique needs. In any case, Zillow knows all too well the best way to increase its market share and accelerate site traffic by winning over the group of professionals who drive the industry in the first place. If Zillow Pro for Brokers' recent progress is any indication, it appears Zillow is succeeding on that front like never before.