Facebook’s fight against fake news has gone global. In Mexico, just a handful of vetters are on the front lines.

After fact-checkers repeatedly flagged Amor a México’s content as problematic, Facebook this month punished the page with its highest-level “demotion,” dramatically reducing its likes, shares and other interactions to 17,000 on June 3 from 121,000 four days prior. Still, Amor a México has doubled its followers to 300,000 in the past few months. Facebook said it was investigating the page but declined to share any information about it.

In interviews, executives conceded that determining the origin and motivation of many page operators is too great an effort for a private company to manage. Instead, the focus is on limiting the reach of serial offenders, punishing behaviors without often being able to get to the source. The brunt of Facebook’s news vetting in Mexico falls to a small group of third-party fact-checkers, whose job is to play whack-a-mole — debunking one story at a time, with each taking several days to disprove.