Perth teen still critical after assault

A teenager remains in a critical condition in hospital after being found injured and unconscious on a suburban Perth street following an 18th birthday party attended by about 180 people.

When police found Kuol Akut, 17, lying on the Girrawheen footpath just before midnight on Friday, several people who were standing near him left before officers could speak with them and find out how the boy was hurt.

Kuol, who is from South Sudan, was last seen riding along Hainsworth Avenue on a white BMX, which has not been recovered.

"We ask that anyone with information on its whereabouts to please contact police," Detective Senior Sergeant Tom Mills said.

He said police also wanted to hear from someone who contacted Crime Stoppers on Sunday, providing specific information regarding Kuol.

"We are currently interviewing guests who attended the party, however with an estimated 180 people attending, there are many more we would like to speak to," Det Snr Sgt Mills said.

He said Kuol's father was extremely distressed.

Kuol's uncle Bol Riak said: "If you know something that happened on the night - Friday night, 11.20pm - if you saw it, please we are asking you to come forward."

In a separate incident around the same time, an 18-year-old man was found on a nearby footpath with head injuries, but was discharged from hospital the next day after treatment.