Joyce Winsie Hu, 15, was killed, prosecutors say, because she gossiped with a friend on Facebook about alleged sexual escapades of another teenager, Radio Netherlands reported.
The trial of the suspects, which began Monday, is being aired to the public, an unprecedented event for a country where cases of juvenile crime are usually heard behind closed doors.
The defendants are 14, 16 and 17 and members of the Chinese community.
The alleged subject of the gossip learned of the scandalous gossip and she and her boyfriend allegedly decided to hire a 15-year-old boy to kill Winsie.
The Dutch Justice Ministry said the pair spent weeks planning the murder, communicating with the alleged assassin by Facebook and telephone. They pressured the boy to kill Winsie, saying if he didn't they would kill him.
Trial for the boy charged in the murder began Monday. The prosecutor wants to sentence him to one year in prison, followed by involuntary juvenile commitment.
Trial for the girl and her boyfriend was to begin this week.