Nasheen Anderson, 17, was charged with Witness Intimidation and Terroristic Threats for allegedly posting information about a 2012 shooting in Southwest Philadelphia on Twitter.
Police also want to know if Anderson ran the Instagram account "Rats 215," which has since been shut down.
The Philadelphia District Attorney's Office said it will be seeking to prosecute Anderson as an adult.
"Witness intimidation has reached near epidemic levels and we are very serious about not only stopping it, but also prosecuting the criminals who are engaging in these despicable actions to fullest extent of the law," said District Attorney Seth Williams in a written statement.
"I don't care how old you are, if you intimidate a witness in this city I'm going to come after you," said Williams.
Investigators previously told Action News that many of the documents and names revealed on the Instagram site are not public record.
They still want to know the source of the information.
