"Don't screw this up," Warren told them, according to one attendee who posted about the visit on social media before deleting it.
She also talked to staff about the importance of the election, including when it comes to issues like filling vacancies on the U.S. Supreme Court and preserving Democratic priorities like the Affordable Care Act and the Dodd-Frank Wall Street Reform and Consumer Protection Act.
The Massachusetts Democrat endorsed Clinton a week ago after remaining neutral during the Democratic primary. Warren's sway among progressives and her willingness to take on likely Republican nominee Donald Trump made her endorsement a coveted one.
But Clinton has also been asked whether she would consider Warren as a vice presidential candidate, a prospect that appears to be under serious consideration. The two met at Clinton's Washington home last Friday, a day after Warren endorsed the former secretary of state.
In a recent interview, Clinton was notably complimentary of Warren.
"I have the highest regard for Sen. Warren," she said in an interview with Politico last week. "I think she is an incredible public servant, eminently qualified for any role. I look forward to working with her on behalf of not only the campaign and her very effective critique of Trump, but also on the issues that she and I both care about."
Other visitors who have stopped by Clinton's Brooklyn headquarters in recent months: New York Sen. Chuck Schumer, singer Jon Bon Jovi, Housing and Urban Development Secretary Julian Castro, former Rep. Gabby Giffords and Former Texas state Sen. Wendy Davis.
Dan Balz contributed to this report.