"Mayor @Michael_Nutter, full $10,000 reward to Nelson Mandela Myers, who saw [the girl] in an Upper Darby park and did the right thing," Mark McDonald, the Press Secretary to Mayor Michael Nutter, tweeted.
Officials say the point of the reward was to get the child to safety as quickly as possible.
"Community policing is about all of us doing the right thing when we see something happening," Mayor Nutter said in a statement. "I commend this good Samaritan, Mr. Myers, for his sharp eye, quick thinking and big heart."
The news came Tuesday night, hours after the passerby spoke to reporters at a news conference at Upper Darby Police Headquarters.
Nelson Mandela Myers, 27, a father of two from Upper Darby, said he was on his way to catch a bus to Norristown, where he works as a sanitation worker, at about 4:40 a.m. Tuesday.
That's when he heard a child's cries coming from a playground near 69th Street and Marshall Road.
"I heard a scream saying, 'Help, help!'" said Myers, who thought at first he was hearing a cat crying.
He went over to investigate and instead found a young girl, cold and upset, sitting under a playground slide.
"When I seen her, she only had a t-shirt on and was wet," said Myers. "She didn't have nothing else on. She was barefooted, she was cold, she was shivering. The first thing came to my mind was, this is a crazy moment right now to see this child out here at this time of night."
Myers said he told the girl to come over to the playground fence, picked her up over the gate, then took his own jacket off and put it around her.
"She said she was cold and that somebody was chasing her and she ran," said Myers.
He immediately called 911 and Upper Darby Police arrived within minutes.
The girl turned out to be the 5-year-old from West Philadelphia taken from Bryant Elementary School Monday morning by a woman dressed in Muslim garb. Police were still looking for that woman Tuesday evening.
Myers said he had not heard about the little girl's abduction or the Amber Alert that had been issued for her Monday night.
He said he and his wife, Janie, are in the process of adopting two foster children, 5-year-old Machia and 3-year-old Gary. Myers said he thought of his own little girl as he held the kidnapped child.
"I am just glad I was there at the right time, because I just wish somebody would do that for my child if my own child was in that situation," he said.
And Myers said he is comfortable with being called a Good Samaritan.
"I can see them calling me that," he said, smiling. "I am a good guy, a humble guy. I just wanted the same thing somebody would do for my child."
Upper Darby Police Chief Michael Chitwood called Myers a hero.