Aadil Shaaid Kahn, 17, Allegra Rose Dahlquist, 17, Drew Logan Shaw, 16, and Ryan Patrick Hare, 18, are accused of killing Silliman. They were ordered held without bond by a judge on Thursday.
According to Silliman's Facebook page, the suspects were all his friends.
Silliman was first reported missing by his parents on Nov. 26 and authorities had issued a Silver Alert for him. He was last seen less than 10 miles from the crime scene.
Medical examiners say they have not confirmed a cause of death. They are releasing few details, only saying the murder took place on Nov. 30.
