Police are investigating the online material believed to be used to make a toxic concoction of alcohol and energy drinks that led to the death of a 15-year-old girl this week.

Paris Kamper, from Kenthurst in Sydney's north-west, was taken to Westmead Children's Hospital on Friday night after consuming a "lethal" amount of alcohol and being fond unconscious at her home.

After clinging to life for nearly three days, the teenager died on Monday morning.

Paris Kamper, 15, was found unconscious and alone at her home in Kenthurst. (9NEWS) (9NEWS)

Police have since seized items from the semi-rural home, including a bottle of alcohol and energy drinks and are investigating the use of online material which may have influenced the excessive amount of alcohol consumed.

The Hills Police Area Command Superintendent Rob Crithlow called the incident "tragic" and said it was based on an "ill-informed experimentation".

"Upon arrival at the hospital, we were informed that her blood alcohol content was .40, which is understood to be well in the lethal limit for alcohol consumption," he said.

"The family are deeply in shock, they've had a terrible weekend of course... doctors and nursing staff did their best to keep her alive, the young lady was under sedation across the weekend and it was clear on Sunday that she wasn't going to recover."

The youngster loved the animals on her farm in Sydney's north west. (9NEWS). (Supplied)

A relative of the teenager has told 9NEWS Paris may have consumed a bottle of vodka with sour lollies in it before she was found.

The 15-year-old has been described as a "lovely young girl".

"The information we have is that she was quite a character, quite a free-spirited young girl, who was well respected and well liked," Supt Critchlow said.

"She was deeply engaged in her animals, she had chickens and horses and other livestock on her semi rural property."

Police say the girl had a blood alcohol level 'eight times' the legal limit (9NEWS) (9NEWS)

Police say the young girl had little experience with alcohol and they will investigate how she located the lethal recipe.

"Anyone who thinks making an instructional video on how to consume excess amounts of alcohol in a dangerous manner is sensible or desirable they need to stop it," Supt Critchlow said.

"The young girl has died alone, in a place that should be safe and it's really pointless, there's no need for this."

Emergency medicine specialist Gordian Fulde said a full bottle of alcohol could kill an adult, let alone a teenager.

"Put simply a bottle of vodka drunk by a big burly adult can kill that adult," Dr Fulde said.

"So once again, what one gets on the internet and all those sort of things really are not necessarily good information."

Medical expert Doctor Penny Adams said that alcohol and the teenage brain create a 'lethal combination' that can change the way of thinking of a young person. (9NEWS) (9NEWS)

Medical expert Doctor Penny Adams also told TODAY this morning that alcohol consumption and the way that a teenager thinks make a "lethal combination".

"There's large amount of alcohol and you mix that with teenage thinking and you dress up this recipe to make it sound like fun - and that's the lethal combination," she said.

"We know that at a greater blood alcohol level of above 0.36, you don't breath, you go unconscious and you stop breathing. So, that blood alcohol level (of 0.40) was incompatible with life.

"Alcohol in teenagers damages their growing brain. It damages the areas involved in learning and memory and with judgement and planning.

"We also know that long-term, alcohol can lead to mood changes which predispose you to depression and anxiety as an adult."

Tributes have since been flowing for the teenager on social media, with her sister describing Paris on Facebook as a "beautiful" person.

Another friend posted on Facebook saying she was "the best friend a girl could ever hope for".

A post-mortem examination is due later this week.