The force is investigating a suspected widespread fraud case in which scammers contact members of the public, falsely claiming to represent companies and promising to recover money and investments.
The force said two companies - WJ Edwards and WJ Investments - are being used by fraudsters to target victims.
The Financial Conduct Authority (FCA) has issued advice on its website that WJ Edwards is not an accredited or registered company.
People from the two firms are known to contact members of the public, falsely claiming to represent legitimate companies including NBSA Ltd, Charles Dickins Ltd, and ECX.
They reportedly claim they can recover or reinvest investments previously made by the members of the public, if they pay the suspects a fee in advance.
Once the fee is paid, no service is performed and the money is kept by the company.
"It is estimated that victims could potentially be in the thousands," a City of London Police spokesperson said in a statement.
"NBSA Ltd, Charles Dickins Ltd and ECX are providing full and thorough assistance to the City of London Police with the current investigation, and hope to seek justice for those who have been targeted and lost money as a result," the force added.
A special investigation has been launched into the incident, named Operation Willow.
City of London Police urged anyone who has been contacted by either WJ Edwards, WJ Investments or individuals claiming to be from NBSA, Charles Dickins Ltd or ECX who have said they can recover money and assets on their behalf, to contact the force immediately.
To submit information, people are asked to contact the City of London Police by completing a questionnaire on the Major Incident Public Portal (MIPP).