The incidents added to a growing awareness of the complicated — and powerful — automated advertising systems that have turned Facebook and Google into two of the world’s most valuable companies. The companies have learned how to maximize their ability to connect any size of advertiser to highly tailored groups of people who use their services every day, collecting billions of dollars in the process.

But the potential misuse of those tools has become a national concern in the past year, particularly after Facebook disclosed last week that fake accounts based in Russia had purchased more than $100,000 worth of ads on divisive issues in the lead-up to the presidential election.

“It’s shocking because it’s illustrating the degree of targeting that’s possible,” said Eli Pariser, the author of “The Filter Bubble: How the New Personalized Web Is Changing What We Read and How We Think.” “But I think the critical piece of context is this is happening when we know that a foreign country used targeted Facebook ads to influence opinion around an election.”

He added: “Before all of this, you could see the rise of targeted advertising, you could see the rise of social politics, but the conjunction of the two in this way feels new.”

Facebook’s self-service ad-buying platform allowed advertisers to direct ads to the news feeds of about 2,300 people who said they were interested in anti-Semitic subjects, according to the article by ProPublica. Facebook’s algorithms automatically generated the categories from users’ profiles.