Tania Clifford, aged 18, was reported missing from West Park, Leeds, on November 4, 2016, just a day after she was discharged from the city’s Becklin Centre mental health facility. She was found hanged the next day.
The Independent Office for Police Conduct investigated West Yorkshire Police’s efforts to search for her.
It found a failure to conduct an adequate risk assessment and a failure to properly review information about Ms Clifford’s personal circumstances and concerns about her mental health.
It found that two unnamed officers - a police sergeant and an inspector - had a case to answer for misconduct.
IOPC Regional Director Miranda Biddle said: “Our investigation found that more could have been done to search for Ms Clifford after she was reported missing.”
Its investigation finished in August last year but the findings have only now been published, after an inquest into Ms Clifford’s death concluded last week, with coroner Jonathan Leach recording a narrative verdict.
The police sergeant was later found to have committed misconduct and was subject to “management action” by West Yorkshire Police, a spokesman said.
The inspector retired before the misconduct proceedings could be held.
While the IOPC did not say this retirement had been inappropriate, it had called on the force to improve the communications between its human resources and professional standards departments to make sure proper processes were followed around retirements during ongoing investigations.
Assistant Chief Constable Catherine Hankinson, of West Yorkshire Police, said the force had voluntarily referred the case to the IOPC.
She said they accepted its findings in full and had acted upon them.
She said: “This was a tragic case in which a vulnerable lady sadly took her own life.”