Police investigating the separate fatal stabbings of two 17-year-olds have made a number of arrests.

The Metropolitan police said on Friday that a second male had been arrested on suspicion of the murder of Jodie Chesney, who was stabbed in the back as she socialised with friends in an east London park last week.

The force said a 17-year-old male was in custody after being arrested in London on Friday morning.

Jodie was in a park in Harold Hill on 1 March when she was approached by two males and knifed from behind in a seemingly motiveless attack. Police said a 20-year-old man arrested in Leicester on Tuesday remained in custody on suspicion of her murder.

Separately, officers arrested four males: two 15-year-olds and two others aged 17 and 18 on suspicion of murdering a teenager in West Kensington, in the west of the capital.

The victim, named locally as Ayub Hassan, was found with stab injuries to the chest in Lanfrey Place on Thursday afternoon.

At the scene of the stabbing, a family friend, Amina Osman, said of Ayub: “He had ambitions, he was looking forward to being a barrister. He was looking forward to being a grown-up man. He was good with his words, he was very kind and handsome.”

There have been growing calls for urgent action to be taken to tackle knife crime across the UK. Police have called for a reverse in the cuts to the number of officers under austerity measures, but the chancellor, Philip Hammond, told forces on Thursday to refocus their existing resources.

Separately, an 18-year-old man was arrested on Thursday on suspicion of murdering 26-year-old David Steven Martinez-Valencia, Scotland Yard said. The Spanish-Colombian man is believed to have been fatally stabbed in a home in Leyton, east London, on Wednesday, before dying in the street.

“At this stage it is understood the victim and suspect were known to each other. The incident is not thought to be gang-related,” the Met said.