HSBC is attempting to make contact with customers who have not used their bank account in more than 15 years.
The high street bank is writing to 12,000 customers and is attempting to track down a further 5,000 as it tries to reunite them with more than £24 million.
Carlos Wanderley, general manager of HSBC's Customer Propositions, said: "We are planning a sustained campaign of correspondence, active tracing, advertising and publicity."
"We will also be conducting research into the primary causes of account dormancy," he added.
Of the 17,000 people on HSBC's list, 5,000 are no longer available at the last address they gave to the bank.
More than £9 million is held in just 276 of the dormant customer accounts, with seventeen having balances of more than £100,000.
Data released from the British Bankers' Association shows 486,670 people accessed its dormant bank account website in February of this year, an increase of more than 180,000 compared with January's figures.
