The police said that the attack was unprovoked
The incident happened at about 1930 GMT in Pilrig Park on Tuesday.
Lothian and Borders Police said the victim was subjected to verbal racial abuse by four young white males and then punched and kicked to the ground.
The boy's headwear came off and the youths cut his hair, an act deeply offensive to Sikhs because of the religious importance of their hair.
The gang ran off across the park, exiting into Pilrig Street and heading in the direction of Leith Walk.
Rab Singh, vice-president of the Sikh Gurdwara in Edinburgh, said: "We are not allowed to get our hair cut.
"So for someone to cut a Sikh person's hair off is very serious.
"For what purpose it has been done, we won't be able to tell until we find the perpetrators."
He said the victim's family are "obviously upset" about the attack.
"When the youths took the knife out, they could have done anything to him," he said.
"He just closed his eyes and hoped that his attackers wouldn't do anything."
Chief Inspector Keith Chamberlain said: "The manner of this crime, where and how it has happened and the legacy that will be left from it is exceptional.
"I want to reassure all members of the community, and the Sikh community in particular, that I'm confident we'll have a positive outcome."
Police have said those responsible for the attack were aged about 16 and descriptions of each of the four suspects have been released:
- The first was 5ft 10in tall. He had brown eyes and was wearing dark Adidas tracksuit bottoms, a dark coloured thick hoodie and a dark coloured beanie hat, possibly Adidas
- The second had a gold hoop ear piercing on his right ear. He was wearing a black Helly Hansen jacket and a dark coloured beanie hat
- The third suspect was was wearing dark clothing
- The fourth had blue eyes, a long sharp nose and facial hair. He was wearing a dark coloured Adidas tracksuit and a white beanie hat
When it was happening all over
Now it’s in our own backyard, people are worried - and it seems only because they realize it might happen to them...
Another reason to GET UP and educate people around you so they know the significance of kesh, who Sikhs are etc
This can be seen as another rude awakening as to why we need to prepare for anything/everything that’s out there.