South Yorkshire Police said a post mortem examination of Conley Thompson revealed no suspicious circumstances.
He was found on Monday morning on the building site in Bank End Road in Worsbrough, Barnsley.
Detective Chief Inspector Dave Stopford, the Senior Investigating officer, said: “The results of the post mortem suggest that Conley had, by some means, entered a vertical pipe on a nearby construction site and was unable to get out.
“Conley’s weight caused him to fall further into the pipe and pushed his clothing up around his body restricting his breathing.
“There is no suggestion of any third party involvement.
“Our job is to now piece together Conley’s movements on Sunday evening and establish how he accessed the construction site.
“Forming part of that investigation we will continue to work with the Health and Safety Executive and our thoughts remain with the family and friends of Conley at this extremely difficult time.”
Conley was last seen in Locke Park – a 40-minute walk from home – at about 20:00 on Sunday.
He had gone to play with friends at the park and was due to return home, but police were alerted when he did not turn up about two hours later.
DCI Stopford said: “The construction site, where Conley was sadly discovered by construction workers this morning, was checked by officers during the hours of darkness and found to be securely locked with a large perimeter fence.”
Howard Civil Engineering is understood to have been carrying our foundations work on the housing job for Erris Homes.
Work underway last week on the site where Conley was found