SAN FRANCISCO — Late last summer, YouTube users began noticing a surge of ads for an obscure news outlet called The Epoch Times. One ad touted an exposé of “Spygate,” a baseless conspiracy theory alleging that President Barack Obama and his allies placed a spy inside President Trump’s 2016 campaign. Another praised Mr. Trump’s interest in buying Greenland as a shrewd strategic move. A third claimed that the opioid epidemic in the United States was the result of a chemical warfare plot by the Chinese Communist Party.

“Anyone else getting a lot of Epoch Times ads?” a user on a YouTube-themed Reddit forum wrote.

“Every other ad on YouTube is a commercial for The Epoch Times pushing Trump,” wrote a Twitter user.

The ads, which sometimes ran for several minutes apiece, were a potpourri of right-wing polemics wrapped in “subscribe now” appeals. They seemed to be everywhere, running alongside videos of pranks, sports highlights and gaming streams. They claimed that The Epoch Times was “America’s fastest growing newspaper” and that, unlike the biased mainstream media, it would provide readers with the unvarnished truth.

The Epoch Times is one of the most mysterious fixtures of the pro-Trump media universe. It was started 20 years ago as a print newspaper by practitioners of Falun Gong, the persecuted Chinese spiritual practice. In recent years, the paper has made inroads into top Republican circles. Mr. Trump and his advisers have shared Epoch Times articles on their social media accounts, and last year, Lara Trump, the president’s daughter-in-law, sat for an interview with an Epoch Times editor. Representative Paul Gosar, a Republican from Arizona, called it “our favorite paper.”