Police say there has been a dramatic increase in synthetic cannabis being sold online since the drugs were made illegal last month.
A man has been arrested in Christchurch and police had ordered the deletion of two social media pages.
Christchurch field intelligence officer Constable Darren Sims said there had been a "dramatic increase" in the availability of illegal substances on social media sites.
"Police are receiving information on a regular basis from members of the public who are keen to help and are passionate about getting drugs off our streets and out of our community," he said.
"We have identified and spoken to people selling and offering to sell drugs on social media sites and warned them about their actions," he said.
