Officers were called at around 7.40am on Thursday to Hanworth Park, Feltham, and found Tyler Donnelly who had been stabbed.
On Sunday, three men aged 21, 27 and 32, were arrested at different locations in London and have been taken into custody, the Met Police said.
Officers have released information that Donnelly left his home around 9.10pm on Wednesday, travelling by bike along Elmwood Avenue before entering the park.
Police are specifically looking to speak to anybody who may have seen anything whilst travelling along Elmwood Avenue, spotted any individual or groups on bikes, or used the H25 bus route passing during the period.
Donnelly was wearing dark clothing and was riding a grey bike when he left his home, but did not return.
Detective Chief Inspector Brian Howie, leading the investigation from the Met’s Homicide Command, said: “Tyler left his home around 9.10pm on Wednesday evening and rode his bike along Elmwood Avenue and at some stage entered the park. He never returned home.
“If you were in the park and saw something, regardless of the reason you were there, please get in touch. Our focus is on what happened to Tyler and who was responsible.
“Similarly, if you were driving through Elmwood avenue, returning home or out walking, did you notice anything? Did you see anyone else in the park on bikes alone or in a group? Did you perhaps see Tyler, who was wearing dark clothing, riding his grey bike?
“The H25 bus route goes through Elmwood Avenue, were you travelling through this area on Wednesday or in the early hours of Thursday? Did you see Tyler or anyone matching his description?
“Tyler’s family and friends are inconsolable after receiving the worst possible news imaginable – our thoughts are with them and they are being supported by specialist officers.”
Anyone with information or footage relating to this incident can also call police on 101 or Tweet on ‘X’ @MetCC quoting 1197/25JAN.
To remain 100% anonymous call the independent charity Crimestoppers on 0800 555 111 or visit crimestoppers-uk.org.