Liechtenstein has issued an international arrest warrant for a former bank employee over the alleged theft of client data.
Liechtenstein will demand Mr Kieber's extradition if he is arrested abroad
The data is being used in a giant tax evasion probe in Germany and several other countries including Britain.
The Liechtenstein police said on their website that they are looking for Heinrich Kieber, a 42-year old former employee of LGT Bank.
Police posted a photo of Mr Kieber, showing a balding man with glasses.
"Mr Kieber is subject to an international arrest warrant. The Liechtenstein law enforcement agencies demand his immediate extradition," the statement said.
The police statement also referred to media reports that Mr Kieber was issued with a new identity and travel documents by German intelligence.
Germany launched its tax inquiry after reportedly paying 5m euros ( $7.7m; £3.8m) in January 2006 for a list of wealthy Germans with money stashed away in the tiny Alpine principality that has tight bank secrecy laws.
The UK's tax authority, the HMRC, has confirmed it also paid an informant for data regarding UK citizens who have accounts in tax haven Liechtenstein.
Investigators in the US, Australia, Italy, France, Sweden, Canada, New Zealand, Spain and the Czech Republic are among other countries hunting for taxpayers hiding their money in Liechtenstein.
'Uncooperative tax haven'
Authorities in Liechtenstein have condemned the purchase of what it says is confidential bank data.
LGT Treuhand, part controlled by the principality's royal family, claims the list of 1,400 customer names are contained on DVDs that were copied by Mr Kieber in 2002.
The data concerns about 1,400 clients, with close to half resident in Germany, the bank said.
Liechtenstein's ruler - Crown Prince Alois - has also argued that Germany's investigation is illegal.
But German prosecutors say their investigation has so far netted 163 people and led to the recovery of more than 27m euros in tax revenue.
The Organisation for Economic Co-operation and Development lists Liechtenstein as one of only three states remaining on its blacklist of "uncooperative tax havens".