Southern Highlands Province police commander Teddy Tei said the gang of women attacked the schoolboy just outside the provincial centre of Mendi on Friday.
"This is a serious matter and police are trying to identify who these animals are," he said.
The boy went to hospital for treatment, he said.
Commander Tei said he feared the women might have infected the young man with HIV/AIDs.
"HIV/AIDs is a problem in PNG and I am concerned the women might be infected.
"I always warn the women to be careful at night but I am now warning the men too.
"Police are investigating but it is not clear why the attack happened," he said.