The development, relief and campaigning organisation is aiming to complete the search in April, with a view to launching the campaign by the end of the summer.
Oxfam has signed up celebrities including Chris Martin, the lead singer from the band Coldplay, the UK garage star Miss Dynamite, Helen Fielding, the author of Bridget Jones' Diary, the actor Colin Firth and Mark Owen, a former star of the boy band Take That.
The campaign forms part of Oxfam's wider Fair Trade initiative, which aims to get poor producers a fair price and help them work their way out of poverty.
Oxfam's Fair Trade campaigning has had notable victories in the past.
Last month, Nestle agreed to drop a £3.7 million claim against the Ethiopian government after Oxfam instigated a campaign against the Swiss food giant.
Nestle backed down and agreed to £930,000, which it is donating to famine-relief efforts in Ethiopia.
BMP DDB is Oxfam's agency of record. It is not known if the agency will be involved in the pitch.