Police have released further CCTV footage as part of their appeal to trace a missing teenager.
Adam Pickup, 17, from Stockport, was last seen on camera in Manchester city centre at about 3.30am on Saturday.
He had been on a night-out with friends and left Fab Cafe in Portland Street about 10 minutes earlier.
He is then seen walking alongside an unidentified couple in Oxford Street who police are still urging to come forward.
Police also want to identify four other people who were sighted on CCTV walking nearby.
Two men, aged 24 and 25, from Manchester, have been arrested in connection with the investigation and remain in police custody for questioning.
But detectives insist it remains a missing persons inquiry unless new information comes to light.
Chief Superintendent Nick Adderley said: "It is extremely out of character for Adam not to return home or communicate with his family and friends, and concerns for him are growing as time goes by.
"We are urging anyone with any information about Adam's movements in the early hours of Saturday to come forward.
"There has been a huge amount of support to find Adam and we are grateful to the public for their help so far.
"In particular, we want to trace the couple and others in the CCTV. If this is you or you know who it is, then please get in touch.
"As part of our inquiries we have made two arrests. I would like to stress that it is not clear what involvement, if any, they may or may not have had in relation to Adam so we would ask the public not to speculate.
"These two men will be interviewed so we can find out if they know anything about Adam's movements.
"While we cannot rule out foul play, this remains a missing person inquiry and our priority is to find Adam."
Adam is described as white, 6ft 2ins, slim with mousey brown hair.
He was wearing a maroon long-sleeved collared shirt, black jeans and black leather Nike trainers with white soles.
The couple in the CCTV footage are described as being white, both with dark hair and wearing dark clothing. The man appears to be wearing glasses and a blue scarf.
Anyone with information about Adam's movements or whereabouts should contact police on 0161 856 9675, or the independent charity Crimestoppers, anonymously, on 0800 555 111.