The incident took place on Saturday night and the girl is currently battling for life at the state-run Goa Medical College and Hospital (GMC) for suspected drug overdose.
After the matter came to light on Monday, police arrested one Shamim Mohammed, 30, from Carrasvaddo, Mapusa and an alleged drug supplier Tukaram Savlo alias Nana in connection with the case.
According to Anjuna Police Sub-Inspector Vijay Kanth Kavalekar, Mohammed allegedly drugged and raped the girl, who was staying at a guesthouse there alongwith her friends.
The victim was subsequently shifted to GMC and her parents were called, who reached here and filed a complaint with Anjuna Police.
"While it was initially suspected to only be a case of drug overdose, a medical examination of the survivor on Tuesday revealed that the girl had been sexually assaulted as well. We have added a section of rape under 376 of the Indian Penal Code," the police officer said.
Yesterday, a court sent Mohammed and Savlo to police custody for three days, according to him.