A 14-year-old boy has been arrested on suspicion of supplying class A drugs in connection with the death of 13-year-old Carson Price.
Carson, of Hengoed, Caerphilly, died after being found unconscious in Ystrad Mynach Park last Friday.
Gwent Police said the boy was arrested at Pontllanfraith, near Blackwood, on Thursday morning.
He is being held at Newport Central Police Station and will be interviewed with an adult present, the force said.
Police said on Monday that drugs were involved in Carson's death.
A form of MDMA, known as Donkey Kong pills, is also a line of inquiry and Gwent Police are trying to trace Carson's movements prior to his death.
Det Ch Insp Alun Davies: "Since the tragic events of Friday evening, our investigation team have been conducting many lines of inquiry to establish the circumstances surrounding the death of 13-year-old Carson Price.
"As a result, this morning, Thursday 18th April, specialist Gwent Police officers executed a warrant under the Misuse of Drugs Act, at an address in Pontllanfraith, Blackwood.
"A 14-year-old boy from the area has now been arrested on suspicion of supplying class A controlled drugs.
"He currently remains in police custody at Newport Central Police Station and will be interviewed with an appropriate adult as part of our investigation."
Supt Nick McLain thanked members of the community for "support during this tragic time".
"The information received from the public has been a vital part of the investigation," he said.
"I would like to emphasise no-one has been charged with any offences and the investigation is still continuing.
"I'd like to ask the community to support our ongoing work and refrain from posting any comments on social media that may jeopardise the investigation."
In a statement over the weekend, Carson's family described him as a "bright and caring, kind and loving, he was a cheeky little boy".
Police said earlier this week that a community outreach team - made up of youth workers who discourage young people from committing anti-social behaviour - were in the park on Friday.
But it is not known whether they came across or spoke to Carson.