The survey by the child protection agency ECPAT International shows perpetrators are most likely to be family members or a close family friend.
It was a small study but showed children were being abused for profit at an appalling rate, according to the director of ECPAT International New Zealand, Eleanor Parkes.
"We saw again and again in this research that more often it's not a "stranger-danger" situation.
"More often it is coming from someone that is known to the child so a family member or a close family friend," she said.
Researchers surveyed 84 welfare workers in Fiji, Solomon Islands, Papua New Guinea, Vanuatu, Tonga, Samoa and Kiribati.
Eighty percent of them had managed cases of child sexual exploitation in the past year.
"It's sexual abuse that has a particular commercial aspect to it, so there's someone profiting from that abuse," Ms Parkes said.
Factors impacting on children's vulnerability include poverty, religious beliefs, culture and shortcomings in the justice sector.
Increasing access to the internet and technology in the Pacific was making children more vulnerable to sexual exploitation, the study found.
The lack of awareness about where the offence lies when it comes to technology was concerning, Ms Parkes said.
"People know that it's illegal to take photos or videos of child sexual abuse but there was much less awareness around the fact that the third party, that person who watches the videos or accesses those images, are also committing an offence and that's on the increase as well," she said.
The study also pointed to more opportunities for exploitation because of increasing trade and travel in the region.
Child sexual exploitation was happening around remote logging camps, set up by foreign companies, according to some of the welfare workers.
Ms Parkes said raising awareness among parents and within communities is crucial to encourage children to speak up about exploitation.
ECPAT has come up with several recommendations including awareness campaigns and training for parents and specialised police units.
Its report also recommends challenging the culture of silence and taboo around sex to get people to report abuse and seek help, particularly in tight-knit communities.
"One thing that was coming through in this research is that when things were reported they tended to get followed up on.
"The rates of an investigation and even a conviction were higher than I expected to see at least. So that's may be reassuring," Ms Parkes said.