The woman was walking in the Cairns central business district at about 10 a.m. on Wednesday when the boy sexually attacked her, The Guardian reported.
She quickly called the police for help but was attacked by three other teenagers who are now being looked for by police, Daily Mail reported.
She reportedly sustained minor bruising and scratches to her face following the assault.
The boy was charged with sexual assault, common assault and assault occasioning bodily harm whilst in company, police added.
Cairns, a popular tourist destination, is home to the Great Barrier Reef and Wet Tropics World Heritage Rainforest.