The attack happened at the victim's home on April 22, police say, after the two met on Whisper, a social media app that allows users to post photos and video messages anonymously.
"This is new to us, this app," said Haverford Township Police Chief John F. Viola. "In fact, our detectives just found out about it themselves."
Investigators say the teen thought she was talking to someone her age. She later discovered the suspect was much older when the pair linked up at her home.
Tina Scott is a psychotherapist who works with kids who have dealt with similar situations.
"I hear the stories every day," Scott told Action News. "Teens coming in here... being assaulted from being on these apps. And their parents only find out after the injury has taken place."
The suspect is described as a white male in his early 20s, with buzz-cut blonde or reddish hair and a stubble beard.
He was 5'7" tall with a stocky build and blue eyes. He was wearing a blue short-sleeve shirt, black shorts, brown Timberland style boots and a gold chain around his neck.
The victim said the man smelled of cigarettes and used the name Joe.
"The person who committed the crime deleted all of the information right away as soon as he left the victim," said Viola.
Whisper, which offered its assistance, is working with police to track him down.
Anyone with information is asked to contact Det. Mark Johnson at firstname.lastname@example.org or call 610-853-1298 ex. 1234.
Meantime, the incident raises concerns about Whisper and other dating apps.
None the parents we spoke with were familiar with the app. Lisa Snopkowski of Havertown has two teen daughters.
"I would probably reiterate to them the whole thing about safety and meeting people online," she said. "You never know who you are going to meet."
"As soon as you get a handle on one thing, there's another thing coming along," said Michael Wilson, also from Havertown. "It's just very tough."
Even the teens we asked either hadn't heard of Whisper or didn't use this lesser-known social media network.
"I know a couple of people that do it, but don't get myself involved in that," said Kalief Mims of Upper Darby.
"I wouldn't use it, because even on Instagram and Facebook and all that I'm not trusting the people that I'm seeing, because people could be using fake pictures of anything," said Anyeyah Burrell of Upper Darby.
Authorities urge everyone to exercise caution and common sense when using dating apps such as Whisper.
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