The body of teenager who had been stabbed to death was found by early morning joggers in west London.
He is the first teenager to be killed in London so far in 2024.
Tyler left his home in Feltham around 9.10pm on Wednesday evening and rode his bike along Elmwood Avenue.
At some stage he entered the park, but never returned to his family.
Detective Chief Inspector Brian Howie, from the Metropolitan Police’s Homicide Command, said: “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.”
He added: “If you were in the park and saw something, regardless of the reason you were there, please do 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 perhaps see Tyler, who was wearing dark clothing, riding his grey bike or did you see him with anyone?
“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?
Scotland Yard said: “Police were called at 7.40am on Thursday, January 25 to reports of an unresponsive man at Hanworth Park.
“Officers attended. At the scene the body of 19-year-old Tyler Donnelley was found. He had been stabbed.”
Tyler’s next of kin were notified, but formal identification awaits.
A post-mortem examination will conducted in due course.
An extensive crime scene remains in place at the park and is expected to be the case for some days to come.
There have been no arrests.
Chief Superintendent Sean Wilson, leading policing in Hounslow, said: “It saddens me to see another young life so needlessly cut short and I urge anyone who has information about who is responsible to get in touch with the investigation team.
“I know that this incident will be a shock for those living and working in the area and my officers will be conducting additional patrols to provide reassurance to the community.
“If you are worried or have concerns please do approach those officers or get in touch with your local neighbourhood policing team.
“I thank you for your patience and understanding as our specialist teams work at the scene and make their enquiries.”
Anyone with information or footage, can call police on 101, quoting 1197/25JAN.
To remain 100 per cent anonymous call the independent charity Crimestoppers on 0800 555 111 or visit crimestoppers-uk.org.