Manchester City footballer Joey Barton has appealed for his brother to contact police investigating the racist murder of black teenager Anthony Walker.
Joey Barton said on Tuesday: "You must do this because you know it's right."
Eighteen-year-old Michael Barton and Paul Taylor, 20, are wanted for questioning by detectives who think the pair could have left the country.
A man, 26, was still being questioned by police on Tuesday. Three men, 29, 18 and 17, have been released on bail.
Joey Barton said the murder was "horrific" and "senseless", adding those responsible "must be brought to justice".
The 22-year-old footballer said the killing of Anthony Walker, who was attacked with an axe in Huyton, Merseyside, on Friday, "shocked the country."
Anthony Walker was taken to hospital but died later
"My sincere condolences go out to Anthony's family," he said.
"My side of the Barton family are sickened by his death.
"Although I was not brought up with Michael, I urge him to come forward and give himself up to police.
"Michael, if you have any information about what happened you have to tell the police.
"You must do this for the Walker family so they can mourn Anthony and because you know it is the right thing to do."
Anthony's sister said she forgave his attackers.
Dominique Walker said "we have to forgive" the gang who used an axe to kill her 18-year-old brother.
Anthony was killed after he was subjected to racial taunts while waiting for a bus with his 17-year-old girlfriend and a cousin, Marcus Binns, also 17.
The three walked away but were followed into a park where Anthony was attacked and an axe was left embedded in his skull.
He was taken to hospital but died later.
Anthony's sister, quoting from the bible, said: "Seventy times seven we have to forgive, that's what Jesus said. So we have to, we have to forgive.
"The only thing left to do now is to catch them."
Anthony's mother, Gee Walker, visited the scene of the attack where a makeshift shrine has been set up.
Dominique Walker said she would forgive the attackers
Among the tributes was one believed to be from his cousin Marcus, who managed to escape and returned to the scene to try to help Anthony.
The card read: "I'm sorry this had to happen. I'm sorry I couldn't protect you."
Books of condolence will be opened at St Gabriel's Church on Hall Lane, Huyton, and at the church Anthony attended, Grace Family Church in Aigburth.
Members of the public can also sign books of condolence at local council offices.
People have been asked to leave flowers and messages at the church.
Meanwhile, Det Ch Supt Peter Currie, who is leading the murder hunt, said police had received more than 50 calls about the killing.
He added: "I would like to reassure the community that we will not rest until those responsible for taking Anthony Walker's life are brought before the courts."