Since the start of 2014, insiders at Trulia have sold $28 million of stock, with CEO Peter Flint unloading $11.2 million in shares, according to the Securities and Exchange Commission. In reference to the insider sales, Trulia spokesman Matt Flegal said the company can't comment on rumors or speculation.
Zillow has a market capitalization of $5.8 billion compared with about $2 billion for Trulia.
Zillow insiders, meanwhile, have sold $69 million in shares since the beginning of the year. The company's CEO, Spencer Rascoff, has unloaded $19.9 million in stock. Rascoff declined to comment to CNBC. He still owns a significant stake in the company through options.
Earlier Thursday, Bloomberg reported that Zillow is seeking to buy rival Trulia, citing people familiar with the matter. Shares of both companies soared on the news, with Zillow up 14 percent in late trading and Trulia up 32 percent.
Thursday's gains follow strong performances for both stocks over the last several months. So far this year, Trulia has risen 52 percent while Zillow has gained 76 percent.
It's unclear why executives who had knowledge of a potential deal would unload their shares. After the recent sales, Rascoff doesn't own any Zillow shares directly but Flint owns 1.3 million Trulia shares in his name. It's possible both executives hold shares through other vehicles.
Sales by Zillow insiders have been fairly steady over the last couple of years, while Trulia's insider sales picked up sharply in late 2013.
—By CNBC's John Jannarone..