The accounts have provoked suspicion. In January, it appeared that the accounts had changed hands; one that had belonged to a “Leo” had changed its display name and handle to Ciera. A “Rick” had become a “James,” and a “Michelle” had transformed into a “Sarah.” (Critics of the account occasionally call them the “Borg,” a reference to an alien race in Star Trek who operate as a collective hive mind.)

Tweets from the ambassador accounts suggest that workers shift in and out of their social media roles. In May, for instance, an account that now uses the handle @AmazonFCBrianDJ tweeted a picture of a smiling man holding an Amazon package and announced that, after four months of tweeting, it would be his last day as an ambassador. About a week later, the account posted a picture of a different man who introduced himself as Brian D.J., an outbound picker at a fulfillment center in Jacksonville. The next month, an account using the name Mary Kate announced that she was returning to her role as a “picker and learning ambassador on the weekdays and modern dancer on the weekends.”

Alex Newhouse , a data analyst at a California gaming company, ran a simple analysis on the accounts and found that about 50 with the naming convention “amazonfc” in their handle were also using a social media management tool called Sprinklr. (Such tools are common for social media professionals; The New York Times uses one called SocialFlow.) Amazon confirmed that its ambassador accounts use Sprinklr.

Amazon is not the only company that relies on what publicists call “employee advocates.” Lizz Kannenberg , the director of brand strategy at Sprout Social, which advises companies on social media use, said that employee advocacy had developed over the last three to five years.

The practice emerged as an alternative to influencer marketing, in which popular accounts on social media are paid to hawk products or recommend services.

“People who work at a company are like the people you’re trying to reach,” Ms. Kannenberg said, adding that they are an “extension” of a brand’s identity rather than endorsers of products. But using employees to address criticism was “something I haven’t seen done successfully before,” she said.