More than one million employees are thought to be affected, the Swiss German 10vor10 news programme reported on Thursday night.
“On average each account holds 7,500 Swiss francs, but there are also accounts with more than 1 million Swiss francs,” Max Meili, head of the national Substitute Occupational Benefit Institution, told the programme.
Meili said that all contact had been lost with almost 70 percent of account holders.
The funds were often forgotten by employees when they changed jobs, or went on maternity leave.
In Switzerland when someone changes job it is their responsibility to transfer their occupational pension to the new company’s pension provider or to a vested benefits account.
Should they fail to do so, the money is transferred to the Substitute Occupational Benefit Institution after two years.
Meili said every effort was made to trace account holders, but it could be difficult to find their current address if they had moved house several times.
Around half of the 6.3 billion Swiss francs is thought to belong to seasonal workers who have left Switzerland.
Anyone with pension funds to claim can seek assistance from the 2nd Pillar Central Office.