Investors who originally bought shares through Pacific Continental have complained to the FSA that they are being cold-called by firms offering to buy the shares, or to put them in touch with a buyer for a fee.
The firms offer to buy shares at an attractive price but demand an advance fee and as soon as the fee is paid the firm disappears with the money and without purchasing the shares.
The regulator says the firms are often calling from outside the UK, are not authorised by the FSA and are not permitted to approach UK consumers to promote financial services.
Pacific Continental went into administration in June 2007 and is now in liquidation.
The FSA says it is looking into the complaints.