According to investigators, the girl told them this was a "prank" committed with a friend at her school, and she never had any intent to harm anyone.
The case is being forwarded to the District Attorney's Office, police say.
RELATED: Extra security ordered in Spring ISD after threat hoax
Authorities say this investigation continues.
There were at least two accounts on which threats were posted. It wasn't immediately known if the teen was behind both accounts.
Parents were alarmed after learning several of the threats specifically mentioned Philadelphia schools.
"That's disgusting. That's very scary," said Cathy Everett of South Philadelphia.
"I think they're very sick people," said Teresa Anastasio of South Philadelphia.
RELATED: Clowns in America. A timeline of scares and sightings
Those are some of the responses Action News received about an Instagram post made through an account called Clown_of_Philly.
The post, which appeared Saturday, warns of a shooting attack at a local school.
It states, "Coming to Neuman Goretti on Monday!! Going to shoot all the students and teachers."
By Sunday night, word had spread. Action News sampled reaction at an Italian festival taking place a few blocks from Neumann Goretti.
"I'm a little nervous. Once again, it's such a close-knit community that we don't let that happen," said Pete Sapienza of South Philadelphia.
"Social media is getting out of hand now. We need to stop and think before we post stuff," said Anastasio.
Another post that was gaining momentum Sunday was from an account called phillyclown.215.
It threatened students at Northeast Charter High School.
The post stated, "We coming to all north east charter high schools.... we will be after your let out on Wednesday."
A second post from same the account says, "the gang is in philly..." and "ya'll ain't safe. it's 12 of us yaheard."
But late Sunday or early Monday that account user posted again, saying "the clown joke is officially over."
To school officials and police, none of this has been a joke.
In the meantime, neighbors in South Philadelphia say they'll be keeping an eye out.
"The neighborhood would never let it happen because it's such a close and tight community. It would definitely be stopped," said Sapienza.
Last week, the Toms River Police Department said security is being stepped up at schools in their area due to reports of clown sightings.
The department offered some background into the clown sightings.
As some of you may be aware there is a story circulating around the nation regarding "creepy clown sightings." The initial reports seem to stem from an organized movie promotion and have now morphed into copycat reports throughout New Jersey. The recent social media posts and threats to schools seem to originate from outside of New Jersey. Facebook shares and retweets have brought these concerns to New Jersey.
In Schuylkill County, Pottsville police received a report of two men, dressed as clowns yelling at children at a playground on Monday, and then took off in a vehicle.
In South Carolina, police increased patrols after new reports of a person dressed as a clown trying to lure children into the woods in South Carolina.
Three children at an apartment complex told police the clowns tried to attract them with money in Greenville County.
The week prior, a mother in South Carolina called police after her son, and others around a different apartment building, claimed they saw clowns behind a basketball court.
"I thought my child was seeing things, and then the next day I had about 30 kids come up to me and say 'did you see the clown in the woods?' " said Donna Arnold.
A teenager in Coffee County, Tennessee, claimed to be attacked by a clown in recent days. The Tennessee Highway Patrol issued a warning to residents about clowns trying to lure children into the woods.
In Reading, Pennsylvania, police say someone in a clown mask was involved in a teenager's killing.
Police say they're sorting through various accounts of the incident that include the victim wearing the mask, the stabber wearing the mask and someone else wearing it.
In nearby Martinsburg, Blair County, police have charged an 18-year-old man with harassing, threatening and prowling around his neighbors' home while wearing a clown mask and holding an Airsoft toy pistol.