The group said it had notified the FBI about a possible embezzlement, which it believes involves a member of the US office of its subsidiary Bite, which looks after clients including Microsoft, Nokia and Sony.
Next Fifteen, which specialises in the technology sector, has hired corporate investigations firm Kroll to look into the fraud, a process which it says will take four weeks.
It had been due to report its full year results on 6 November.
The company said that the issue has had no impact on underlying trading and that it expects to report full year earnings in line with market expectations.
Next Fifteen’s shares rebounded somewhat to finish 5.76 per cent down.
“In the final stages of the audit, Next Fifteen has learned that it has been the victim of a complex fraud involving a senior member of the finance team in its Bite North America subsidiary, and as a result the company has chosen to delay its results pending a full investigation, which it expects to be completed in the next four weeks,” the company said.