He did so, court papers allege, by pushing the message that they would have a reasonable probability of success if they bought into the investments, that Trump was promoting them because of that decent chance of success, and that he had researched the businesses before making his endorsement.
"The Message was materially false," the suit says.
"Defendants were aware that the vast majority of consumers would lose whatever money they invested in the business opportunities and training programs the Endorsed Entities offered."
"The Trumps conned each of these victims into giving up hundreds or thousands of dollars — losses that many experienced as devastating and life-altering," the suit claims.
"By defrauding so many for so long, the Trumps made millions."
The suit, filed in U.S. District Court, has four individual plaintiffs, who are all identified with pseudonyms.
But it seeks to recover damages for anyone affected by the defendants' actions as alleged. In addition to Trump and the Trump Organization, the defendants are Donald Trump Jr., Eric Trump and Ivanka Trump.
One plaintiff, a Pennsylvania woman identified as Mary Moe, according to the suit, signed up with ACN in April 2013 after being recruited at a meeting where she saw a "a promotional video prominently featuring Trump's endorsement."
"Moe was moved by Trump's statement that there was a huge potential to make money with ACN," the suit said.
After paying the nearly $500 registration fee, Moe "spent nearly two years working hard to pursue this business opportunity, buying and studying training and promotional materials," pitching the products and attending meetings, according to the suit.
"At every meeting, organizers reminded participants about Trump's involvement," the suit said. "But despite her hard work, Moe was not able to make money, and ultimately she realized that she had been misled by Trump's endorsement."
The suit is being funded by a nonprofit group, the Tesseract Research Center, whose chairman is a Democratic donor, Morris Pearl, according to The New York Times, which first reported the court action.
The White House, the Trump Organization and the Tesseract Research Center did not immediately respond to requests for comment by CNBC.
In a statement issued to the Times reacting to the suit, the Trump Organization said:
"This is clearly just another effort by opponents of the President to use the court system to advance a political agenda."
"Not only are the allegations completely meritless, but they all relate to events which took place nearly a decade ago and are well past the statute of limitations. It is also quite telling that the plaintiffs and, more importantly their political activist attorneys, each of whom have longstanding and deep ties to the Democratic party, waited until just over a week before the midterm elections to file this suit even though they have been obviously planning and working on this for months."
"The motivations here are as plain as day."
But a spokesman for the plaintiff's legal team told CNBC, "This case is being brought now because it is ready now. We did a thorough investigation and a lot of legal research, and the plaintiffs are eager to file."
"No matter when this was filed, the Trump Org would say it was politically motivated," the spokesman said.
The spokesman also said, "This case does not fall outside of the statute of limitations. Filing today allowed us to ensure that was the case and that all the victims could get justice."