The arrest Thursday evening follows the arrest of four other boys, all between 14 and 15 years old. All have been charged with Rape, Criminal Conspiracy, Simple Assault and related offenses.
Two of the boys were arrested on Wednesday while the other two were arrested earlier in the day on Thursday.
The attack happened Monday around 7:30 p.m. at the Francis Myers Rec Center at 58th Street and Kingsessing Avenue.
Police say the 12-year-old was in the center's computer room when the teens lured her into a third floor stairwell and raped her.
Action News spoke with the victim's father earlier this week.
"I'm full of anger. I'm full of disgust that this has to happen in our neighborhood at a rec center where every child should feel safe," the father said.
Action News is not naming the father to protect the daughter's identity.
"She said she was pulled into a fire escape by four to five boys," the father said.
Volunteer coordinator Omar Jordan says his assistant saw some teens running away from the stairwell.
"Then he went upstairs to see what happened and he found the 12-year-old girl up there crying and shaking saying she was raped," Jordan said.
Investigators say the victim didn't know the suspects personally, but had seen a couple in passing in recent weeks.
"She looked real shaken up, like real scared, she really didn't want to talk to nobody. She tried to vent to us to let us know what happened so we could go ahead and take the next step. And what's the next step is we called the police," Jordan said.
Detectives from the Special Victims Unit took the 12-year-old girl to Children's Hospital of Philadelphia to be examined.
Meanwhile, volunteer coordinators were upset about the incident taking place inside the rec center.
"It's ridiculous, that's why we can never have nothing for kids...these young kids are ridiculous and getting out of control. We need to bring our city back under control," Jordan said.
City leaders are outraged.
"We are outraged, not only that it happened at one of our recreation sites, but that it happened at all," Susan Slawson, Deputy Commissioner of Recreation and Programs, said.
"There's no excuse for four kids deciding to take advantage of another young person; it is not acceptable," Everett Gillison, Mayor Michael Nutter's Chief of Staff, said.
The girl's father sent out a message for his daughter.
"I want her to feel it isn't her fault and that she doesn't have to stand for her rights being violated," the father said.
Many of the city's rec centers, especially the larger ones, are being outfitted for security cameras. Franis Myers Rec Center was in the planning stages.