In the latest case, the white academic told AFP that she was attacked on Friday while conducting research on birds and the impact of climate change in a remote forest on Karkar Island in Madang province.
Police in the capital Port Moresby on Sunday confirmed the attack.
"We have taken statements but no arrests have been made yet," a spokesman told AFP. "This is a very serious incident."
The 32-year-old was walking along a bush track with her husband and a guide when nine men armed with rifles and knives ambushed them, stripping the husband and guide naked and tying them up, she said.
They then stripped her, bound her hands, cut off her blonde hair to the scalp and gang-raped her for about 20 minutes before something in the forest startled them and they ran away.
The guide managed to break free and the three of them fled naked back to the nearest village, several hours away, she said.
The husband and wife returned to Port Moresby on Saturday, where they were met by a photographer working for AFP who helped them file police reports and organise a flight out of the country.
The case was also reported to the US embassy. A duty officer told AFP Sunday that the embassy had no comment to offer.
Violence against women is endemic in Papua New Guinea, but it is rare for a white woman to be targeted, and the academic said she wanted to tell her story to shine a light on the issue.
"This story should not come out because I am white," said the woman, who was on her fifth visit to the country since 2010, often staying for up to four months to conduct research.
"It should come out in hopes that it empowers Papua New Guinean women to stand up and say no more violence against women in this country.
"I hope my story can make a change."
The American's ordeal comes barely a week after Australian Robert Purdy, 62, was shot dead at Mount Hagen, in PNG's Western Highlands, and a woman he was with, reportedly from the Philippines, was gang-raped by 10 armed men.
PNG Prime Minister Peter O'Neill condemned that attack as the "cowardly act of animals".
"This kind of behaviour totally undermines our efforts to make our country a safe destination for investment and tourists," he said.
"We cannot allow the entire nation to suffer because of the behaviour of one or two sick people."
The incidents follow a series of gruesome murders, including a 20-year-old mother who was accused of witchcraft, stripped and burned alive in front of a crowd at a market near Mount Hagen in February.
Earlier this month, an elderly woman was beheaded after being accused of sorcery.