The 14- and 15-year-olds were arrested along with a 20-year-old following the death of Hannah Bragg in Tavistock, Devon, on Saturday.
She was found in a disused viaduct and died in hospital. What is thought to have been ecstasy was recovered near where she was found.
A 14-year old was also taken to hospital after the two suffered what police think was an adverse reaction to the drug.
Officers arrested a 20-year-old man, from Tavistock, on suspicion of conspiracy to supply a controlled class A substance.
A 14-year-old boy was arrested on suspicion of supplying a controlled class A drug.
A 15-year-old boy, from Tavistock, was arrested on suspicion of supplying a controlled class A drug and possession of a controlled class B drug.
Detective Inspector Adrian Hawkins said all three suspects had been released under investigation.
“We are continuing to work towards establishing the cause of events that led to this tragic incident,” he said.
“The local neighbourhood teams are providing a visible presence in the area and schools have also been engaged with on the risks surrounding drug use.
“One young girl’s life has already been lost, the message to the public at this stage is clear: no drugs are safe.
“I would like to stress that this was an isolated incident involving these two young people and we are continuing to investigate the extent of drug use and supply throughout Tavistock.
“We would, however, urge all parents and carers to speak to their children and young people about the risks of taking unknown substances.
“Our thoughts and prayers remain with the family and we continue to provide support to them at this terrible time.”