Police are appealing for information after a 16-year-old boy was attacked outside a college.
Six men, including one with a knife, approached the student near Redbridge College in Barley Lane, Goodmayes, on January 16.
He was attacked but the knife was not used and he was left with bruises to his face and body.
The boy was treated at King George Hospital in Goodmayes.
The men are said to have warned the victim not to tell police about the attack, telling him the man with a knife would stab him at his home if he told anyone.
The boy informed police that the same group of men robbed him in December.
Two men were arrested and bailed until March 14.
Police are still looking for the four remaining suspects.