COLLINGSWOOD — A Florida man told police he was "following his heart" when he traveled to South Jersey and Philadelphia to have sex with a girl he knew was just 12 years old, authorities say.

Liam Heim was charged with first-degree kidnapping on Saturday after he was found with the missing girl from Collinsgwood at a hotel near Philadelphia International Airport.

According to a police affidavit, the 21-year-old-man traveled from from Gulfport, Florida to Collingswood to meet the girl he first encountered in a "dating context" via an online gamer chat system called Discord.

The girl's best friend, identified in the affidavit as "I.K.," tipped police off to her use of the app. The missing girl and Heim had used the app to communicate over the past six week, the affidavit says.

The day the girl went missing, she and Heim went into Philadelphia via PATCO and to a hotel on Bartram Avenue, where they spent the next 36 hours, police said in the affidavit. There, Haim sexually assaulted the girl, police said.

Police tracked Heim's cell phone to the hotel, where they found him with the girl, the affidavit says.

The girl was first reported missing on Thursday night by her parents when she did not come home from school.

Heim was charged with one count of first-degree kidnapping and one count of third-degree endangering the welfare of a child. He was scheduled to make his first appearance in court on federal charges on Monday, and a detention hearing was scheduled in New Jersey on Tuesday.

Discord is a free voice and text chat the company that helps players create relationships built around around playing games, according to the company website. The company said it has 14 million daily users.

The State Police Internet Crimes Against Children Task Force last September told New Jersey 101.5 parents about 26 apps they said make them potentially vulnerable to predators — but warned predators are usually quicker than parents to catch onto new apps and trends.  Task Force commander Lt. John Pizzuro said at the timeany game-oriented platforms where different people can join in on the action are potentially dangerous because you never really know who you’re talking to.

Pizzuro said online predators will frequently make contact on an app and then suggest changing platforms.

David Matthau contributed to this report.

Contact reporter Dan Alexander at Dan.Alexander@townsquaremedia.com or via Twitter @DanAlexanderNJ