Investigators are still searching for four Los Angeles high school students after 10 teens were arrested on and off campus last week in connection with a series of alleged sexual assaults against two underage female classmates that began more than a year ago, police said on Monday.

Authorities said they believe the sexual assaults took place at Venice high school, in west Los Angeles, as well as off campus, starting in December 2013 and continuing until as recently as this month, according to the Los Angeles police department.

On Friday, the LAPD announced that investigators had identified 14 suspects in connection to the case. That morning, LAPD detectives, joined by Los Angeles school police department, arrested eight students on campus, and one student off campus. A 10th student turned himself in to police later that day. The arrested teens range in age from 14 to 17.

“We are still actively looking for those four individuals,” said LAPD detective Kimberly Porter said on Monday.

Porter said investigators have not yet located the four male teens identified in connection with the case. She said it’s still unclear if the four are students at Venice high school or if some or all have moved to other schools.

Those arrested were booked on charges of either unlawful sex with a minor or forced oral copulation, Porter said. During a press conference on Friday, LAPD commander Andrew Smith said some of the crimes were forced sexual acts, and others were consensual with victims too young to legally give consent.

The alleged assaults were first reported to school administrators, who immediately contacted the police department’s special assault section about a possible sexual assault. An investigation was opened on Tuesday, and the arrests began on Friday. Porter said she could not say who reported the alleged sexual abuses, whether it was one of the alleged victims or other students.

The Los Angeles Times reported that students alerted school administrators about the possible sexual abuse, citing a senior district official who declined to be identified. The newspaper reported that students directed administrators to “video or photos related to the case that had surfaced on social media”.

The Times also reported, citing anonymous sources, that several boys were present during some of the acts, and that they “had threatened the girls with harm to their reputations if they did not comply”. The paper also reported that some of the accused teens were student-athletes who played on the school’s football and basketball teams. Porter said she could not confirm either report, but said investigators are looking into the circumstances of the alleged instances.

Porter said detectives are actively searching for photos, videos or social media postings of the alleged assaults, though she couldn’t say what, if anything, they have found so far. Producing and distributing sexually explicit content involving minors is illegal, and she said investigators would look into that as well.

Authorities have only provided general information about the string of possible assaults because of the sensitive nature of the alleged crimes and the ages of all involved. Porter said both alleged victims have been interviewed extensively and that precautions were being taken to protect the girls, who are students at the school.

In a statement, the Los Angeles Unified school district said it was cooperating with the investigation. The district’s superintendent, Ramon Cortines, said officials had notified the students’ parents, and crisis counselors had been made available to assist students.

“This is a painful moment for Venice high school and this district,” Cortines said in a statement. “I want you to know that no sexual misconduct of any kind by students or staff will ever be tolerated in LA Unified.”