North Shore residents are calling on police to monitor social media sites to shut down youth beach parties before they get out of control.
Rampaging youths smashed bottles all over Castor Bay residential streets on Saturday night after police arrived.
Residents' letterboxes and council signs were used to fuel a beach bonfire.
But residents believe the gathering was arranged and assembled faster than it took police to disperse alcohol-fuelled revellers.
Devonport-Takapuna Local Board chairman Chris Darby said social media such as Facebook was used to organise people on the night to keep one step ahead of police.
One Facebook entry he had seen declared: "Castor Bay is where it's at."
Saturday night's event mirrored one at Cheltenham Beach the previous Saturday, said Mr Darby.
Police did not disperse the crowd until several hours after residents gave the alarm about unruly behaviour and damage to private property.
Police said the crowd numbered about 250 people but residents said it was double that.
"They had a bonfire on the beach and were ripping branches off pohutukawa trees to burn them.
"They were thumping on doors and invading private property.
"I hope police are monitoring the social media because feedback suggests young people are doing instant messaging that's getting people to events pretty quickly."
Mr Darby said the board would ask police how it could support them.
"These are our young people in the community. They are our kids."
At Castor Bay, worried residents called police at 9.20pm, saying a gathering at the small beach was out of hand.
When police arrived at The Esplanade, a group threw bottles at them.
As more carloads of youths arrived in the cul-de-sac, police blocked a number of streets in the area. Helped by observers in the Eagle helicopter, they dispersed revellers into Beach Rd.
"It took a couple of hours to spread them out and move them away and quiet things down," said Senior Sergeant Matt Rogers.
"No arrests were made and nobody was hurt."
At the Cheltenham incident, four arrests for disorderly behaviour were made.
Yesterday morning at Castor Bay, as broken glass on the street was swept into piles, residents were still shaken by the scene.
"I estimated about 200 youths," said one man, who asked not to be named.
"I called police because I could see things were getting out of hand and the cars were arriving.
"I want to know why it took a good two hours before they acted.
Another resident said: "We watched as it totally erupted and they converged here because police were marching up, yelling 'Go home or be arrested' and the helicopter came in with its strong lights.
"Police did a wonderful job when they did come."By Wayne Thompson Email Wayne