Letting agents are creating fake adverts of properties against a background of strong demand and insufficient supply.
BBC London says its investigation found one agent using exactly the same photographs for three properties in different locations.
The BBC also found one home owner who found her own flat listed on Zoopla without her knowledge.
She only discovered it because she wanted to remortgage and looked up the value of her property on the portal.
She found it had been listed as available to let a month earlier by an agent in Islington.
She said: “It’s our home. We’ve been here for so long, and to see someone creating a deception around our address feels like our home has been stolen to a certain extent.”
BBC London quotes David Cox, managing director of ARLA, who said that “ghost listing” is on the rise.
He said: “We’re hearing anecdotal evidence that this is increasing.
“It’s in all parts of London from the high-end properties in central London to average-priced properties in east and south London.
“It’s because the agents don’t have the stock. There is a massive shortage of housing and a huge influx of people.”
Cox told the BBC that policing “ghost listing” is almost impossible.
He said: “These listings will look exactly the same as any genuine listing. Unless someone actually notices ‘that is my property’ they’re probably never going be found.”
Legal guru David Smith described the practice as “bait and switch” – agents advertise a property that does not exist, and then tell prospective tenants of another.
He said: “If someone is induced to see a property that doesn’t exist, they then may be so desperate by that point they’ll take an inferior product they would never normally have taken, or they’ll be prepared to pay too much money for it.
“People are already talking about how the market in London is overheated. This just distorts it further.”
Rightmove and Zoopla both told the BBC that they are aware of the problem, and remove content that is not genuine.
The BBC’s latest coverage follows a You and Yours programme in the summer where a home owner found her property on an agent’s website. We reported on it here
The BBC’s story also follows EYE’s coverage of so-called portal juggling this week, whereby agents re-list properties.
All three of the main portals did not consider it a major problem – but an astonishing number of our readers admitted to it, or could point to its prevalence.