Acting Police Commissioner Christine Coulter says cops have been getting tips from the public and are pursuing leads. But she's hoping to hear more.
"How could they not get involved when children are being shot and children are being murdered?" she said. "I mean, if you don't stand up at any time in your life, it's now to say that this is just unacceptable."
She said she believes people know the "cowards" who pulled the trigger.
She was killed on Sunday when someone used an assault rifle to fire six bullets into her home on Water Street near Ontario. Her mother, who was holding the girl at the time of the shooting, and a man who was cleaning carpets in the house were injured.
"These little kids that are innocent, and they're just dropping like flies," said Rivera's aunt, Camile Pagan.
The intersection of 34th and Water streets was flooded with family and friends, mourning the loss of the toddler.
"She lost her life. We are burying a child," Pagan said, "not an adult that's lived, that has had experiences. This child isn't experienced enough."
Pagan wants anyone who knows anything about the shooting to come forward. "You giving them information helps," she said, addressing those gathered for the vigil. "Justice for Nikolette at the end of the day. Doesn't matter what beef you had with the person on the next block. It doesn't matter."
Neighbors standing in solidarity with the family, holding pink and white balloons, agreed she was full of life. Rivera's babysitter remembers the toddler as joyful.
"She loved music and fashion and getting her makeup done," she said.
"Always laughing and always smiling," said a neighbor.
"Yes, a star, for real," said another. "She's gonna be a star right here today. Watch."
Pagan blamed easy access to guns for the growing violence in Philadelphia.
"It's too easy to buy a gun and too easy for them to be using them the way they are out here," she said. In a seperate incident on Saturday, an 11-month-old boy, Yazeem Jenkins, was critically wounded in Hunting Park when shots were fired into a car he was riding in. So far, police have made no arrests in either shooting.