The song, "Don't Let Me Down," is being considered as the first single release from the X Factor winner's next album, according to the Sun newspaper.
"IFPI is working with SyCo and law enforcement agencies in the U.S. and Europe to trace the individuals who stole the Leona Lewis/Justin Timberlake track," said Jeremy Banks, head of IFPI's Internet Anti-Piracy Unit.
"The police investigation is ongoing," he said in a statement. "Such pre-release leaks, however they are sourced, are highly damaging to our members who invest considerable budgets in marketing and promoting music ahead of release."
The music industry has seen revenues slump in recent years amid rampant Internet piracy in some regions, and the rise in legal digital downloads has failed to make up for losses in physical music purchases.
SyCo is music promoter and television talent show judge Simon Cowell's division of Sony Music Entertainment, which signs up acts who appear on The X Factor show in Britain.
Lewis won The X Factor in 2006, and her debut album "Spirit" topped charts around the world. Her second album is slated for release in November.