Joshua Johnston pleaded guilty to obtaining $3 million through a false investment scheme at Wellington District Court on Monday. (file photo)

A fraudster who obtained $3 million in a fake investment scheme may have more victims.

Wellington man Joshua Johnston has pled guilty to a months-long scam, leading to three charges of obtaining by deception in Wellington District Court.

Johnston took $3 million from three people he asked to invest in an audio-visual contract and leasing work in the Waikato, offering dividends.

Police suspect he may defrauded more than five others through a range of scams, including false investments in stock and currency.

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Detective Daryl Gera​ is asking other victims, or those who believe they are owed money, to come forward before Johnston's sentencing on August 31.

Johnston's fraud had people convinced of the success in their investment by providing some returns - until the returns stopped coming.

He had victims across the country.

"It sounds like there's so many victims that we're unable to get that information from him," Gera said.

"The outstanding victims aren't going to increase the loss by millions of dollars, possibly by hundreds of thousands."

People who committed such offences could be cunning and determined to take people's money, he said.

"It was really good that they did come forward, because that meant that we were able to prevent it happening to other people."

"There should be no shame in any victim of financial crime coming forward."