Volunteers began collecting signatures at midnight.
On Sunday, volunteers were set to take part in a Freedom from Filner March and Rally at city hall in downtown San Diego.
"This march is for the people to send a message that Mr. Filner must immediately resign or be removed from office," said rally spokeswoman Kathryn Vaughn, a San Diego attorney and workshop leader on sexual harassment in the workplace.
Recall petitions were being circulated at the finish line of the 36th annual America's Finest City Half-Marathon and 5K Run/Walk in Pan American Plaza in Balboa Park.
A third daytime civic event was also planned.
More than 100,000 signatures are needed to get the recall on the ballot. Organizers have until Sept. 26 to submit the necessary signatures.
Sixteen women have accused Filner of sexually harassing them.
Filner has apologized for what he says was inappropriate behavior and acknowledged disrespecting and intimidating women but has said he is not guilty of sexual harassment.
The San Diego City Council is also investigating Filner's use of the city's credit card, which has been frozen. Documents show he's racked up $11,000 in charges paid by taxpayers, and has only paid the city back for one charge.
CNS contributed to this report.