Founder of craigslist Craig Newmark attends The Rush Philanthropic Arts Foundation's Annual Rush HeARTS Education Luncheon on March 11, 2016 in New York City.

Craigslist could be raking in $1 billion a year, according to one researcher's estimates, signaling strong growth for the online classifieds company despite new challenges from tech giants.

Craigslist has seen threats to its core business in recent years, with the launch of Facebook Marketplace and in the wake of a congressional sex trafficking law that resulted in the removal of personal ads from Craigslist. Smaller mobile challengers like LetGo and OfferUp have also dented traffic to Craigslist.

But price hikes on in-demand ads have nudged annual revenue past $1 billion, according to AIM Media Group, a digital marketplace consulting group.

AIM estimates Craigslist brought in $1.034 billion in 2018, an increase of nearly 50 percent from 2016 revenue — the most recent year for which AIM conducted its research. AIM projected annual revenue for Craigslist of just $7 million when it started studying ads in 2003.

"Craigslist is the No. 1 classified advertising site in the world, both by revenue and by traffic," said founding principal of AIM Media Peter Zollman. "It's stunning that a single site can generate $1 billion in revenue, with more than 99 percent of that coming from the United States."

Craigslist doesn't disclose revenue figures, and the 50-person company is owned entirely by its founder, Craig Newmark, and CEO Jim Buckmaster. AIM estimates annual revenue by counting ad placements in representative markets.

Craigslist declined to comment for AIM's research and did not immediately return a request for comment from CNBC.

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