Ms. Harder had been senior VP-client director of the Publicis Groupe network.
While a client director, Ms. Harder led the Celebrex media team and was recognized with Effies for campaigns for South Beach Diet's "Life on the Beach" and the National Cattleman's Beef Association.
In her new position, she will continue to lead work for Mattel and will oversee digital integration, agency training and new and organic business growth for the Los Angeles office. MediaVest's West Coast clients include E Networks, Style, G4 and Mattel.
Ms. Harder joined the Starcom MediaVest group in 1986 as part of Leo Burnett's media department.