The incident happened at about 6pm on Saturday 1 November 2014 as the 15-year-old boy was waiting at a bus stop next to the Manchester Gallery opposite George Street.
The teenager was wearing his camouflaged uniform having spent the day in the city center selling poppies and collecting money to commemorate Remembrance Day.
As he was looking down Princess Street for his bus, he was approached by a black man who, without warning or provocation, produced an aerosol can and a lighter which he used to spray lit fumes in the direction of the unsuspecting teenager.
Shocked at what had happened, the Cadet suffered minor reddening to his face and Singed hairs on his face and right forearm.
Without saying a word, the offender walked off. He is described as being black or Asian, 5ft 8in tall and wearing a dark hooded top. He appeared to be under the influence of alcohol and was staggering.
Police have now issued CCTV footage of a man who was seen in the area shortly before the attack and are keen to trace this man.
Detective Inspector Liam Boden said: “It is now nearly a week since this attack and we are continuing to pursue a number of lines of inquiry to trace whomever was responsible for this appalling assault a 15-year-old boy.
“We have now released CCTV footage of a man we really want to talk to as part of our inquiries. This man was seen in the vicinity of the attack shortly before it happened and we believe he may have crucial information. We are treating this man as a key witness and if you are that man, then please come forward as soon as possible and speak to us.
“This attack has prompted worldwide media interest and there has been a lot of speculation about possible motive. I want to be clear that we are still keeping an open mind about what motivated the offender. It is impossible to get inside the mind of the offender but I do want to reassure people who may be alarmed that we believe he may have been under the influence of either drugs or alcohol and no comments were made that suggested it was religiously or racially motivated. I also want to stress there have been no other attacks of this nature since.
“Nevertheless, this was a very serious incident that left a courageous young man shocked and upset and we need to find the offender, so I would urge anyone who has information to come forward.”
Anyone with information is asked to call police on 101 or the independent charity Crimestoppers, anonymously, on 0800 555 111.