Thousands of Americans attended a march last November organized by a Russian group that used social media to interfere in the 2016 election.

The demonstration in New York City, which took place a few days after the election, appears to be the largest and most successful known effort to date pulled off by Russian-linked groups intent on using social media platforms to influence American politics.

Sixteen thousand Facebook users said that they planned to attend a Trump protest on Nov. 12, 2016, organized by the Facebook page for BlackMattersUS, a Russian-linked group that sought to capitalize on racial tensions between black and white Americans. The event was shared with 61,000 users.

As many as 5,000 to 10,000 protesters actually convened at Manhattan's Union Square. They then marched to Trump Tower, according to media reports at the time.

The BlackMattersUS-organized rally took advantage of outrage among groups on the left following President Trump's victory on Nov. 8 to galvanize support for its event. The group's protest was the fourth consecutive anti-Trump rally in New York following election night, and one of many across the country.

"Join us in the streets! Stop Trump and his bigoted agenda!" reads the Facebook event page for the rally. "Divided is the reason we just fell. We must unite despite our differences to stop HATE from ruling the land."

While the focus has been on Russian efforts ahead of the election, the BlackMatters rally days after Trump's victory shows that Russian-linked social media influence efforts continued after the election.

The BlackMatters organizing group was connected to the Internet Research Agency, a Russian "troll farm" with ties to the Kremlin, according to a recent investigation by the Russian Magazine RBC. Facebook has identified the Internet Research Agency as the group responsible for purchasing 3,000 political ads on Facebook's platform and operating 470 accounts that appear to have attempted to influence the perspectives of Americans during the 2016 elections.

Facebook has since deleted those 470 accounts. BlackMatters's account has been deleted as well, although Facebook has not officially confirmed the reason for BlackMatters being deleted from its site. Twitter also appears to have deleted an account associated with the group, possibly in its own purge of accounts linked to Russian actors.

"This is another example of why it's important to disclose who is paying for promoted posts on Facebook," said Katherine Haenschen, a professor who researches digital media at Virginia Tech.

The march is an example of the types of "organic content" - posts created by users, rather than as ads - that lawmakers are looking for as they investigate the extent of Russian political manipulation of social media platforms. But Haenschen believes Facebook's paid features might have helped the event go viral.

"It also speaks to the challenges of organic reach. It's unlikely that this audience is free or organic," Haenschen said, referring to BlackMatters's Facebook reach which included over 99,000 users who liked the page, according to an archived version of the page from May 16, 2017.

Facebook recently announced that it would introduce new transparency features, including making users who run election ads verify their identities with the company.

Haenschen says that this isn't enough. She argues that this type of event that isn't explicitly about elections could fall through the cracks, and says that Facebook should be aware of all users using the platform's paid features.

For its part, Facebook says that it's trying to make sure that such content stays off its platform.

"The foreign interference we saw is reprehensible and outrageous and opened a new battleground for our company, our industry and our society," says Facebook General Counsel Colin Stretch in testimony he is set to deliver to the Senate Intelligence Committee on Wednesday. "That foreign actors, hiding behind fake accounts, abused our platform and other internet services to try to sow division and discord - and to try to undermine our election process - is an assault on democracy, and it violates all of our values."

Top Democrats in the House and Senate Intelligence committees, Sen. Mark Warner (Va.) and Rep. Adam Schiff (Calif.), have both said that such organic posts tied to paid content will reveal the true scale of the Kremlin's alleged social media campaign.

According to numbers in Facebook's general counsel's leaked congressional testimony, the number of people potentially touched by organic content eclipses the potential number reached by ads by hundreds of millions.

Lawmakers will have the chance to dig into this more when Facebook shares organic posts it has found to be created by Russian actors. Top lawyers from Facebook, Twitter and Google are expected to testify on Tuesday and Wednesday.

BlackMatters had organized other protests, but none revealed so far reached the level of support that the Nov. 12 protest did - in many cases, the organization's events fizzled out and didn't come to fruition. Others that actually did take place had a limited and isolated reach.

Other events that appear to be organized by the group tended to focus on rallies around race flash points, including the deaths of black men killed by law enforcement, The Hill found after reviewing 15 events by the organization. Others claimed to offer free legal education for immigrants.

One event was shared with 1,300 users on Facebook, of which 240 ultimately said that they would attend the "One Person One Vote One March," on Dec. 3 in New York City, a protest against the electoral college. But it's unclear if the event actually occurred and, if it did, how many people attended.

"The Electoral College is an outdated, undemocratic system that does not reflect our modern society, and it needs to be changed immediately," the event description reads. "Every American should be guaranteed that their vote counts!"

Posts on BlackMatters's website also focus on matters of racial justice, highlighting instances of police brutality and racial justice concerns in the U.S.

The group reportedly recruited Americans who were unaware of its links to Russian actors to help its mobilizing efforts and organize these events.

"I thought it was a knockoff of Black Lives Matter," one organizer who unwittingly worked with the group told BuzzFeed, but changed his mind after looking at the group's website, which he thought "looked legit."

The group's social media and digital messaging contrasts with earlier social media activity by Russian actors who may have tried to interfere in the election. Outlets like The Daily Beast have revealed social media activity for Russian-linked groups that attempted to mobilize pro-Trump groups on the right before the election.