Joining a long tradition of companies and campaigns that drop bad news on holidays, Facebook on Thanksgiving eve took responsibility for hiring a Washington-based lobbying company, Definers Public Affairs, that pushed negative stories about Facebook’s critics, including the philanthropist George Soros.

Facebook’s communications and policy chief, Elliot Schrage, said in a memo posted Wednesday that he was responsible for hiring the group, and had done so to help protect the company’s image and conduct research about high-profile individuals who spoke critically about the social media platform. Mr. Schrage will be leaving the company, a move planned before the memo was released.

Facebook fired Definers last week, after a New York Times investigation published on Nov. 14.

“Did we ask them to do work on George Soros?” Mr. Schrage wrote in the memo, a draft of which had circulated online earlier in the week. “Yes.”

He added: “I’m sorry I let you all down. I regret my own failure here.”

[Sheryl Sandberg is said to have asked Facebook employees to examine George Soros’s finances after he criticized the social media giant.]