Two adults and three juveniles have been charged with gang-raping a 7-year-old girl who was sold by her 15-year-old stepsister during a party at a crime-ridden apartment building, police said Saturday.

Details on the arrests were to be announced at a Saturday night news conference at police headquarters in Trenton, the state's capital city.

Police said the girl was offered for sale by her 15-year-old stepsister on March 28.

The teen went to a party with some men on the 13th floor of the Rowan Towers apartment building, and the younger girl tagged along because she worried about her stepsister's safety, police said.

The 15-year-old sold sex to men in the room, then took money to let them touch the younger girl, and the touching turned to forcible sex as at least seven men raped the 7-year-old, police said.

Before the Saturday announcement of the five arrests, the 15-year-old had been charged with promoting prostitution, aggravated sexual assault and other crimes; police have not released her name. A 20-year-old man had been charged with having sex with the 15-year-old.

Mayor Doug Palmer said he met with the victim's relatives at his office on Thursday to offer help and make sure they were able to move out of the neighborhood over safety concerns.

"We made sure they got out of the area," he said Saturday afternoon, before the news conference.

He credited the police force for its hard work but said "we're still not finished." He pledged to spare no expense "to make sure that everyone responsible is brought to justice."

"We're still asking the community to let us know if they have any more information on this heinous crime," he said.

Palmer met with the parents, the 7-year-old girl and her two younger siblings. The woman is the mother of the 7-year-old girl, and the man she lives with is the father of the 15-year-old. The man and woman also have two toddlers together.

He said police officers had taken the case "very personally."

Police Director Irving Bradley would only say "it's still an active investigation."

Police earlier in the week were urging residents to come forward, but neighbors said they were scared of retaliation from gangs that prowl the streets if they spoke up.

Rowan Towers sits on a stretch of West State Street near downtown Trenton and is surrounded by blocks of abandoned, boarded-up homes. It's fronted by a well-manicured lawn and features a colorful playground and a basketball court. An American flag hangs from a pole to the right of the front door.

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Associated Press writer Beth DeFalco contributed to this report from New York.