In a new report released today, the experts -- who monitor a UN arms embargo against Somalia as well as sanctions against accused pirates and Shebab Islamists -- say Facebook has failed to respond to "repeated" approaches.
The sanctions investigators say Somalia's notorious piracy business is supported by accomplices who could be bankers, businessmen, politicians or aid workers "all using their regular occupations or positions to facilitate one or another network.
"Investigations have confirmed that these myriad facilitators are interlinked through various communication channels and employ social network services, such as Facebook," said the report.
The experts said they had "active and comprehensive support" from other private companies with their investigations.
Social media giant Facebook did not immediately respond to an AFP request for comment.