"There is no such level of safe use of a prohibited drug – they (drugs) are very inconsistent, you don’t know what the effects are going to be," he said on Sunday.
"Just don’t take it in the first place.
“We want you to be safe - we are doing literally everything we can do.”
He said the circumstances of the Central Coast teen’s death were now being investigated and would be a matter for the NSW Coroner.
NSW Health confirmed the 19-year-old died following a “drug ingestion”, while another 10 were taken to hospital for treatment.
Three remain in Westmead Hospital in a stable condition, a NSW Health spokesperson said.
The teen is the fifth young person to die at a music festival during the Christmas/New Year festival season, triggering renewed calls for pill testing at gigs.
Assistant Commissioner Jones said pill testing was a "matter for the government" but said the NSW Police Force would roll out a "robust" harm prevention strategy for festivals in March, including extra security.
"We are reviewing these music festivals literally on a daily basis," told reporters.
Earlier this month, NSW Labor leader Michael Daley said his party would explore the possibility of pill testing if it won the March election.
The NSW government has ruled out pill testing, saying it gave people a “green light” to take something potentially dangerous.
“I think the process, as it’s currently being promoted, is fraught with significant risks that will give festival-goers a false sense of security that drugs are safe to use," NSW Police Minister Troy Grant told SBS News last week.
“This (pill testing) is no silver bullet."
An estimated 11,387 attended FOMO, with police officers searching 146 people and finding 54 of them with drugs.
Another 23 revellers were ejected, mostly for intoxication, while 28 were refused entry, police said.
The FOMO festival is now working with police as part of the investigation and a spokesperson told the Sydney Morning Herald organisers were “deeply saddened" by the death of the woman who was "with her family when she died at Westmead Hospital".