"Had a 'visitor' in our backyard this evening by Takapuna Grammar," the suspicious resident wrote.
"As soon as the sensor lights came on he cycled off," they added.
Then came a plea for information, some amateur profiling - and a colourful description.
"Anyone recognise him - short sleeves and no bag on a cold night suggests he might be a local.
"Tallish chubby white male - looks like a ginga moustache. Full black BMX helmet with chin guard. BMX style bike pink/reddish."
They also claimed that police had attended swiftly but could not track the man.
"Yikes, not at all good," another resident wrote.
The mystery masked man. "Bike colour could be his downfall hopefully," a concerned local opined, hoping the lurid bicycle may lead the constabulary to the interloper's door.
"OMG that's Jason Bourne," a fantasist unhelpfully suggested.
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But others raised the possibility that this was altogether more innocent.
"How weird he looks like a dad...bizarre thing to do early evening, could he be looking for something? A dog perhaps," a woman suggested,
There was no dog. Just a lost husband.
"Omg. That is my husband," the mystery man's wife announced.
"Was biking to a friend's house and got the house number wrong. He is chubby - and harmless. Sorry to freak you out!"
She apologised for her geographically challenged husband's wanderings and said the drama will make her "chortle" for days to come.
The drama settled, others rushed to the defence of the well-padded North Shore dad.
"*big boned," a helpful man said.
"I'll pass that on. He will feel better," his wife said.
"He swears he is festively plump - all year round."
Case closed.