Britain's The Sun said the well-worn leather belt disappeared about three weeks ago and the Irish star of "The King's Speech" is offering 16,000 pounds ($24,409) for its return.
"Colin has had this lucky leather belt for so long he just can't bear to get rid of it," the source told The Sun. "The thing is literally coming apart at the seams."
The newspaper said the belt came from Colin's father, Eamonn, a former soccer star in Ireland. It has undergone numerous alterations and repairs over the years.
"Like having extra holes punched in it and extra leather added since he has gone through so many weight changes," the source said.
Farrell has hung on to other articles of "lucky" clothing over the years. He claimed in 2004 to wear a specific pair of shamrock-decorated boxer shorts given to him by his brother every time he starts shooting a new movie.