Police continue to urge witnesses to come forward one week on from the murder of Jamil Palmer in Crane Park, Hanworth.
Officers have renewed their appeal after growing increasingly concerned over "misguided loyalty", in their path to seek justice for the teenager and his family.
Leading the investigation, detective chief inspector Noel McHugh of the Homicide and Major Crime Command unit, said Jamil had left a friend's house in the nearby Butts Farm Estate in Hanworth around 3.15pm and was attacked shortly thereafter.
Mr McHugh said: "Jamil was attacked in Crane Park shortly before 3.30pm and the park would have been busy with people.
"Some witnesses have come forward to assist us with our investigation but I am certain there are a number of other people who have yet to speak to us.
"It is clear that there is a misguided loyalty where some people are not speaking to the police, protecting those involved.
"I would ask those who are reluctant to come forward to do so, so Jamil and family can get the justice they deserve.
"I would also like to reiterate my reassurance to anyone who has witnessed this horrific attack that my officers are here to protect you and will treat any information you have with the utmost sensitivity and discretion.
"The park is popular with dog walkers and other park users - if you were in the area between 3pm and just after 3.30pm and witnessed this incident, or the events leading up to or immediately after the incident, you may hold vital information."
Jamil Palmer of Belgrade Road, Hampton, Middlesex was airlifted to a central London Hospital where he later died.
A post-mortem examination has given the cause of death as a stab wound.
The mother of Jamil who remains unnamed has reiterated her call for help.
She said: "Do the right thing in Jamil's memory. Forget your street code, it is not grassing and it is not cool. Just tell the police what happened and who was involved.
"I've lost my son. The hurt that has been caused is unimaginable.
"All I ask is that you trust the police and come forward. How would you feel if this happened to your love one?"
An 18-year-old man and a 16-year-old boy were arrested on suspicion of murder last Tuesday (6).
Both were bailed to return to police in early June.
The suspects made off in the direction of the A316 Chertsey Road.
Anyone with information should call the incident room on 020 8785 8099 or call Crimestoppers anonymously on 0800 555 111.