The helicopter had to land on the sand and a doctor and paramedic treated the assaulted boy before he was taken to hospital by South East Coast ambulance.
Kent Police said they were alerted to the disturbance at about 17:05 BST on Saturday and inquiries were ongoing.
Reports said it followed a row about a girl, but police did not confirm this.
A police spokesman said the boy's injuries were not life-threatening.
On Twitter, people said several police and ambulance vehicles went to the beach alongside the air ambulance helicopter.
A tweet by @valeriesnatural said: "When it's [too] crowded there is always trouble...... #margate #margatebeach #ilovemargateâ€¦ instagram.com/p/BUmopIxFB_1/"
And @Lucysal wrote: "All of a sudden a massive fight broke out involving loads of teenagers at #Margate beach today."
A brawl involving about 50 young people on Margate beach led to the air ambulance being called to help an injured teenage boy.