A 17-year-old girl is dead after police say she and three friends took ecstasy at a sleepover in Abbotsford, B.C.

Cheryl McCormack died on Thursday, two days after she was rushed to hospital in critical condition because of a negative response to the party drug. Police believe the teen was using ecstasy for weight loss purposes.

"This was not something that was an experimental night. This was something that the girls were familiar with and as a result, maybe got complacent or comfortable with and not fully embracing what can be some of the risks that are involved in any kind of ingestion of illegal drugs," Abbotsford Police Const. Ian MacDonald told CTV News.

The three other girls at the party did not have the same reaction to the illegal substance, but were treated in hospital as a precaution and released the same day.

Investigators are now trying to identify the dealer who supplied the girls with ecstasy and are asking anyone with information to call police.

The Abbotsford Police Department and McCormack's parents have also issued a warning to parents and teens, saying that illicit drugs are inherently dangerous and should be avoided.

"Any time you are ingesting illegal or illicit drugs you don't truly know what's in them and you don't know what kind of reaction they're going to have with your body," MacDonald said.