In 2011, "virtually none" used encrypted sites, but in 2014 that number was 37 per cent.
These sites are found on the dark web, the online black market that requires specific software, configurations or authorisation to access.
Dr Wilkins said Nucleus and Alphabay were two popular options for those seeking and selling illicit drugs, as they offered a range of drug types not widely available in New Zealand.
"These technological advances present new challenges to domestic and international drug control."
A police spokesman said dark nets sites have been a police focus for some time now.
"We know New Zealanders have been purchasing drugs from these sites. Police [are] aware of the risks posed by these sites and [are] adapting strategies and tactics to address them ... on a case by case basis."
Dr Wilkins said the survey also revealed a decline in the use and availability of synthetic cannabinoids following ban of legal highs, and reports that methamphetamine was easier to obtain than ever before.
"Findings ... indicate the bans had a significant impact on the use and availability of synthetic cannabinoids, the most widely used products."
The use of synthetic cannabinoids by ecstasy users declined sharply, from 22 per cent in 2013 to six per cent in 2014 and the proportion of frequent drug users who reported that synthetic cannabinoids were more difficult to obtain leapt from 19 per cent to 57 per cent.
Those who reported the price was increasing rose from 31 per cent in 2013 to 51 per cent a year later, and drug users who said fewer people were using synthetic cannabinoids increased from 36 per cent in 2013 to 70 per cent.
"The findings suggest while synthetic cannabinoids have not disappeared completely, their use and availability is much reduced with the end of the legal commercial market."
He said the increased availability of methamphetamine continued in 2014, particularly in Christchurch and Auckland.
"The proportion of frequent drug users who could purchase methamphetamine in one hour or less increased from 51 per cent in 2011 to 76 per cent in 2014.
"The proportion of frequent drug users who purchased methamphetamine from a gang member increased from 36 per cent in 2013 to 50 per cent."
Dr Wilkins said a number of factors could be behind that trend in Christchurch, including general recovery following the earthquakes, the influx of workers for the rebuild in the city and reported re-organisation of the gang scene, as well as more coming from Australia and around the world.
The police spokesman said police were also seeing increased usage "across the board".
"This year's survey continues to confirm the link between gangs and methamphetamine, which is well known to police. In 2015, police laid 572 charges against gang members and prospects for importation, supply and manufacture of this illicit drug.
"In the same year, police and Customs seized 334.3kg of methamphetamine -- three times the amount seized in 2014."
The current availability of cannabis fell from 2013 to 2014, with a particularly marked decrease in Christchurch, said Dr Wilkins. The proportion who described the current availability of cannabis as "very easy" declined from 62 per cent in 2013 to 45 per cent in 2014.
The spokesman said that the survey was a useful part of the intelligence gathered by police and other agencies about trends in drug use and drug-related harm.
Report findings
• 73% of people surveyed used social media and encrypted websites to buy and sell drugs
• 37% of people used encrypted sites, compared to "virtually none" in 2011
• P is easier to get than ever before
• Half of P users surveyed now bought it from gangs
• 70% reported fewer people used "legal highs"
• Only 6% of regular ecstasy users now use "legal highs" compared to 22% in 2013
• Marijuana is harder to get now that in previous years
Source: 2014 Illicit Drug Monitoring System (IDMS) study, Massey University
