Since Facebook disclosed the existence of those ads and posts with Russian ties last month, the company has attempted to tamp down fears it abetted interference in the election. It has also added rules meant to improve disclosures of political advertising in an attempt to show users exactly who is behind the ads they saw run through their newsfeeds.

And on Friday, the company began a test of new features designed to give users a better understanding of the people and organizations buying advertising on Facebook. That included providing users with a searchable database of ads being served to them.

But misleading ads were often a small component of the misinformation campaign.

Investigators believe the Internet Research Agency, a so-called troll farm that has been linked to the Kremlin, amassed enormous followings for various Facebook Pages that masqueraded as destinations for discussion about all sorts of issues, from the Black Lives Matter movement to gun ownership.

Aided by Facebook’s finely tuned ad-targeting tools, the Russian firm would pay to place posts in the News Feeds of users. The ad product, called a “promoted post,” was designed to look little different than the rest of the content flowing through the News Feed.

Users who responded in a positive manner to the advertisements were prompted to subscribe to related Facebook Pages or Groups run by the Russians. If they did, it meant that nonpaid, “organic” posts would begin to appear in the users’ News Feeds. From there they spread, being shared and reshared among the user’s network of friends.

The tactic was effective. Some of the pages, like “Blacktivists,” which focused on racial issues, had more than 360,000 users who “liked” the page — even more than the main “Black Lives Matter” page.

Facebook is not the only big internet company wrestling with the issue. But at Mr. Zuckerberg’s company, the issue has been particularly troublesome, given how easy it is to spread messages to tens of millions of Facebook users.