Acting Detective Chief Superintendent John Ross of the Metropolitan Police’s East Area Command Unit described the girl’s death as a “tragedy”.He issued an appeal for witnesses to the attack or anything suspicious in the area on Friday night.The officer added that additional patrols would be put in place in the Harold Hill area.The killing comes less than a week after Che Morrison, 20, was stabbed to death outside Ilford train station in east London. Her family said they were too distressed to speak. Friends said Chesney was “the nicest girl possible” Explaining how she had heard voices yelling for help, she said: “I never thought in a million years that I was coming out to a murder and that I would be walking out to a young lady who had been stabbed. “Then a boy said, ‘I need help, my girlfriend has been stabbed’ and I just flew over there.“People are scared to help, but all I was thinking with my mother’s instinct was, ‘I need to help’. Her boyfriend did everything he could.”She placed the girl in the recovery position and administered chest compression in the hope of reviving her.“The knife’s blade was still in her, but I didn’t see it because it was dark,” she continued.“I didn’t realise at the time, but then all I kept thinking, once the police told me, was, ‘Have I put the knife in further by giving her compressions?’“It was horrific, it was just the blood. There was so much of it. The girl was moaning, but she was mostly silent. We checked her pulse and we could hear her breathing.”An ambulance crew arrived, but Ms Farenden believed the girl was already dead by then.She said she was told later by police that the blade was still inside her and was removed at the scene.The girl is the 18th person to be murdered in London this year, five of whom have been teenagers.She was also the fifth person to be fatally stabbed in the capital in just eight days. The grandmother of a 17-year-old girl stabbed to death in an “unprovoked attack” in London has made an anguished plea for the city’s street violence to end.Jodie Chesney was said to have been sitting with friends near a children’s playground in a park in Harold Hill, Romford, on Friday when she was approached by two men.It is understood one of the men was seen to stab her in the back before the pair fled.The A-Level student’s apparently random murder is the latest grim chapter in the capital’s knife crime epidemic.Debbie Chesney, her grandmother, spoke of her anger at the spate of senseless killings.She wrote online: “This was our youngest granddaughter. How have we come to this point where kids can’t have a walk in a park without suffering an unprovoked attack?“We don’t want anyone else to go through what our family is suffering right now.“This has to stop, there are too many young people having their lives cut short by needless violence.”Her granddaughter’s final moments unfolded in the company of friends and nearby neighbours who had rushed to her aid.Teresa Farenden, a 49-year-old mother of three whose home backs onto Harold Wood where the girl was attacked, went to help the teenager after hearing screaming coming from the park shortly after 9pm. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. Friends who congregated at the scene tearfully told how the girl was studying psychology and sociology for her A-Levels.She apparently attended Havering Sixth Form College.The students, who lay flowers near the site where she was attacked, said she was not the type of girl to get into any trouble and was “the nicest girl possible”.A mother who had accompanied her son – a friend of the girl’s – to the scene, said Jodie was with three friends in the park when the attackers struck.“Two of them chased the scumbags and two of them were trying to get help,” the woman, who did not want to be named, said.“I believe it was a random attack. They were just sitting there, they were having a Friday night giggle, as we have all done.“What do you do at 17? You just want to go out and be with your mates and not have your mum tell you to stop making so much noise.“It is an inner city crime that is moving to outer London areas; it was never like this before.”Forensic officers conducted a fingertip search of the area, just yards from a children’s playground.A Scotland Yard spokesman said a murder investigation had been launched and the victim’s next of kin had been informed. No one has been arrested.