Police have searched the flat of Jerome Kerviel, the man said to be the rogue trader who lost 4.9bn euros ($7.1bn; £3.7bn) at Societe Generale.
Police have searched Mr Kerviel's apartment
Officers spent two hours at the address in the Paris suburb of Neuilly before leaving with a number of briefcases.
While Mr Kerviel's exact whereabouts is now unknown, his family has leapt to his defence, insisting he is innocent.
"He is being made to carry the blame and is not the guilty one," one unnamed relative told the Reuters news agency.
While Societe Generale has yet to officially name Mr Kerviel, it has filed a legal complaint against the trader, accusing him of defrauding the bank by making unauthorised financial trades.
The bank's chairman Daniel Bouton said the fraud was a "one-off" and denied it was a trading or risk-management fault.
Mr Bouton also took out full-page advertisements in French newspapers on Friday, in which he asked the bank's shareholders to accept his "apologies and deep regrets".
"I understand your disappointment, your anger," he said.
"This situation is perfectly unacceptable."
'Who was funding?'
As the recriminations continue, both Societe Generale shareholders, analysts and the French government have questioned how the rogue trader was able to operate alone.
Jerome Kerviel, the reported rogue trader
"It is difficult...to imagine how one person alone could, in a relatively short period of time, cause such considerable losses," said French Prime Minister Francois Fillon.
"They are saying all of this was cunningly concealed, but somebody must have been funding the collateral or whatever was needed to sustain those positions," said Derek Chambers at Standard & Poor's Equity Research.
The French government is also angry that Societe Generale did not inform it immediately after the losses were discovered.
French President Nicolas Sarkozy called the events at Societe Generale a "large-scale internal fraud", but added that the losses "do not affect the solidity and reliability of the French system".
Societe Generale said the fraud was based on simple transactions, but concealed by "sophisticated and varied techniques".
SOCIETE GENERALE IN FIGURES
Founded in 1864
467bn euros in assets under management (as of June 2007)
22.5m customers worldwide
120,000 employees in 77 countries
According to reports, Mr Kerviel worked at the bank's Delta One products team in Paris.
He was responsible for betting on the markets' future performance, bank executives said.
Societe Generale said the trader had taken what it called "massive fraudulent directional positions in 2007 and 2008 beyond his limited authority".
Executives said the trader may not have sought personal gain from the fraudulent deals.