The Jacksons accused John Branca and John McClain of faking legal documents prior to the singer's death in June 2009, and Katherine is believed to be in the middle of the dispute over the family's financial affairs.
The Los Angeles County Sheriff's Department confirmed it had been contacted on Saturday after her grandchildren, Paris, Prince, and Blanket were unable to reach her all week.
"I can confirm that a missing person's report was filed this evening by Mrs Katherine Jackson's nephew, Trent Jackson, after he was unable to see her or reach her for a week. The report will be referred to the Homicide/Missing Persons Unit, and they will be handling the investigation," Lieutenant Josh Thai from the police department told US website Radar Online.
A source added that the family are concerned for Katherine's welfare.
"The kids are being taken care of by their nanny. Paris is absolutely beside herself with worry. She lost her father three years ago, and not to know if her grandmother is okay is just more than she can bear," the insider revealed.
Michael's teenage daughter Paris also took to Twitter to ask her followers to contact authorities with any sightings of Katherine.
She tweeted: "Yes, my grandmother is missing. I haven't spoken with her in a week ... I want her home now. If anybody sees my grandmother, please call the authorities or this ... security number. Thank you so much.''
Katherine, 82, left her California home on July 15 to fly to New Mexico with her oldest daughter Rebbie Jackson, her lawyer Sandra Ribera told CNN.
"The kids were trying to get a hold of their grandmother and they haven't been able to reach her for almost a week," Ribera said. "They are told she's unavailable. I'm concerned that she's not safe."
- WENN
