"They try to write in code but it's obvious, writing things like drops offs or door sales.
"I think it's pathetic. We've banned at least 10 people a month."
Rotorua police area commander Inspector Bruce Horne commended this action.
"People underestimate the power they have in the community to effect change," he said.
"The most powerful thing for positive change is when people group together and say what they're going to accept or not accept. It's encouraging that people have taken that stance."
Canterbury District Police have started an initiative aimed at disrupting the spread of illegal drugs in communities.
Staff are monitoring the internet and following up on Facebook groups with letters, visits and in some cases search warrants.
"Anyone who is using the internet to sell or distribute controlled drugs should think twice as police are determined to disrupt these activities," said Canterbury police Detective Senior Sergeant Jason Stewart.
"We recognise addiction to controlled drugs contributes to crime.
"This is about encouraging addicts to seek help and break the cycle of crime."
Anyone from around New Zealand can warn police of illegal activities at any time.