An investigation into sexual misconduct at the Oakland Police Department that began with an officer’s suicide a year ago ended Wednesday with the firings of four police officers and suspensions of seven others.

At a late-afternoon news conference with Mayor Libby Schaaf, City Administrator Sabrina Landreth said the officers are being disciplined in connection with the scandal involving a 19-year-old sex worker from Richmond who calls herself Celeste Guap. Officials have said some officers had sex with Guap, the daughter of an Oakland police dispatcher, in some cases when she was a minor.

Schaaf would not reveal the officers’ names, saying state confidentiality laws barred it.

In addition to the officers who face dismissal and suspension without pay is an officer who was referred to counseling, Landreth said. She said some of the officers have already left the department, but the findings will be placed in their personnel files.

The officers can appeal the disciplinary measures through grievance procedures, the mayor said.

The announcement ended an investigation that roiled City Hall and coincided with the abrupt departures in June of three police chiefs, including Sean Whent, a veteran credited with improving the department. In addition, at least two officers who were being investigated resigned.

The probe began last September with the suicide of officer Brendan O’Brien, who left a note referring to Guap. Guap told The Chronicle that she had sex with O’Brien while she was 17 and that he was the second Oakland officer she had dated when she was underage. She said she had sex with 29 officers from multiple police agencies over the past two years.

Officials said the officers who face dismissal committed at least one of several offenses that included attempted sexual assault, lewd conduct in public, assisting in prostitution, helping prostitutes evade arrest and accessing law enforcement databases for personal gain.

Alameda County District Attorney Nancy O’Malley is expected to decide soon whether to file criminal charges against the officers, the mayor added.

“Today we are affirming our commitment to continue to rebuild trust ... and we send a loud and clear message that we hold our officers to nothing but the highest standards,” Schaaf said.

At the hastily called news conference on the second floor of City Hall, Schaaf was joined by Deputy Police Chief John Lois, who described what he called the “extremely exhaustive and complete investigation” that included 11 interviews with Guap over 20 hours. Investigators also interviewed 50 witnesses and examined 80,000 social media pages and 28,000 text messages, he said.

The mayor said she was “deeply sorry for the harm this incident has caused.”

Guap told The Chronicle a few of the officers paid her, while some of the others tipped her to antiprostitution stings or ran names of people she was curious about through confidential databases. One Oakland officer, she said, had sex with her at a hotel near the Oakland airport in February, then texted her later in the morning to warn of an undercover sting.

“Their perks become your perks,” Guap said. “They have resources. They can run things for you. They can find out s— about anybody. If they can find out s— about anybody, I can find out s— about anybody.”

Schaaf said Wednesday that she did not believe Guap, who was participating in a rehabilitation program in Florida, was aware of the disciplinary actions against the police.

Oakland City Council President Lynette Gibson McElhaney, after hearing the mayor’s announcement, called the action a “strong message” and a “promising first step.”

“Every officer who has to serve has been bruised by this,” McElhaney added.

The council president said she had reached out to Guap but that the young woman “did not welcome our support and help.”

“Whatever the hustle was that she thought she had under control was upended by this,” McElhaney said. “If there’s a silver lining, it’s that she will be a stronger woman and find redemption.”

Also attending the mayor’s announcement was civil rights attorney John Burris, who said he was “obviously pleased.”

“It’s very important to restore integrity to the department, and this goes a long way,” said Burris, who has been involved in the federally mandated oversight of the Oakland Police Department.

Kevin Fagan, Rachel Swan and Steve Rubenstein are San Francisco Chronicle staff writers. Email: kfagan@sfchronicle.com, rswan@sfchronicle.com, srubenstein@sfchronicle.com