Have you seen Nguyen, missing from Sheffield?

Police in Sheffield are asking for your help to find missing 16-year-old Nguyen Viet. 
Nguyen was reported missing on Monday 12 September after he left an address in the Division Street area of Sheffield. 
He was last seen in the city centre at about 1.30pm on Monday and despite numerous efforts to trace him, he has not been seen or heard from since. 
Officers are keen to hear from anyone who has spoken to him or who knows where he might be. 
Nguyen is about 5ft 6ins tall and of slim build. He was last seen wearing a grey shirt, black jeans and grey trainers. He is also thought to be carrying a rucksack. 
Have you seen Nguyen? If you know where he is, please call 101 quoting incident number 712 of 12 September 2016.