Dylan died on January 17th after being hit in the head in an unprovoked attack the day before at the Place Bel Air in the North Vaud city.
Cantonal police on Friday said they have interviewed 18 suspects after arresting them at their homes or at their schools or places of training in an operation that took place over three days earlier this week.
Investigators also spoke to 16 victims of violence, aged 14 to 18, who live in the North Vaud region.
Two of the victims were hospitalized while nine others lodged complaints of threats and assault.
The investigation has found so far that five of the suspects exchanged mobile phone messages to orchestrate random threats and attacks on the victims.
Suspects are accused of punching and kicking victims in the head.
Police officers uncovered fake guns, knives, pepper spray canisters and pellet guns in their search of suspects’ homes.
“The acts were premeditated and it’s serious,” Daniel von Siebenthal, Yverdon mayor told the 20 Minutes newspaper.
The mayor noted that many of the victims have not dared to step forward and that a “law of silence” was impeding the investigation.
Three minors remain in detention over the affair.
Police are urging other victims to contact them as the investigation continues.