Lewis was killed while working a part-time job as security guard in a convenience store near Austin and Division. Police say two masked men stormed in and opened fire, killing Lewis.
The local faith leaders met at the store Saturday to announce the reward and to urge the public to come forward and help police.
The Rev. Ira Acree said ministers and community leaders pooled $2,000 into a reward fund looking for suspects in the Thursday night shooting.
"I want you to know whether it's your son, your brother, your husband or your friend, the blood of this honorable officer is on your hands," Acree said.
The Police Memorial Foundation already is offering a $10,000 reward for information leading to the arrests of the killers. Anyone with information is asked to call 888-Y-PO-SHOT.
Another $1,000 was added, bringing the total reward to $13,000.
"There will be no harbor in this community for the perpetrators of this crime," said the Rev. Marshall Hatch of the Leaders Network
The shooting happened Thursday night when two men robbed the M & M Quick Foods. Lewis, 41, was working security because the store was robbed earlier this month.
According to authorities, Lewis did draw his weapon after the men opened fire but didn't stand a chance. He was hit multiple times.
Lewis' family is devastated.
"We're going to feel lost without him," said Henrietta Fountain, the grandmother of Lewis's daughter. "It's just going to be hard. For everyone that loved Cliff, and I can imagine it's just so many people, it's just a great loss."
Lewis was a highly decorated officer, a father and a soon-to-be husband. He had just proposed to his longtime girlfriend on Christmas day.
Acree said ministers prayed Saturday with the officer's family.
"She's relying on God," Pastor John Collins about Lewis's finace. " She don't understand it, she's dealing with it. It's her faith that is helping her and her family."
(The Associated Press contributed to this report.)