Casey Johnson, 30, the party girl heiress to the Johnson & Johnson fortune, who on Dec. 9 was online showing off the engagement ring she gave Tila Tequila (right), has died in Los Angeles. Her father is Woody Johnson — owner of the New York Jets. Johnson, whose pals include Paris Hilton and Lindsay Lohan, was arrested in November for grand theft. The cause of death is unknown. TMZ reports her body was found this morning in L.A.