Zimmerman was acquitted by a Florida court for the February 2012 shooting death of 17-year-old Martin, who was unarmed.
Jealous says about a million of the signatures collected were sent by cell phone, and many were from young people.
Martin has emerged as a recurring symbol at protests of continued unequal treatment of blacks and other minorities.
His mother was among the speakers at Saturday's events marking the 50th anniversary of the March on Washington for Jobs and Freedom. Images of the slain teenager were displayed on T-shirts, posters, signs and buttons.