The legal team, which has flown out to Portugal, will reveal details of the fund within the next few days.
The lawyers will help with liaison and will not interfere with the inquiry, Madeleine's uncle John McCann has said.
Rewards of £2.5m have been offered to anyone with information leading to the four-year-old's safe return.
Madeleine, from Rothley, Leicestershire, disappeared from an apartment in the Algarve resort of Praia da Luz on 3 May.
A spokesman for the International Family Law Group, the legal company helping the McCanns, said: "Gerry and Kate are very grateful for all the support and generous offers of help that they are receiving.
"Details of how contributions can be made to help get Madeleine back to the safety of her own family will be made available in the next couple of days."
REWARD CONTRIBUTORS
Meanwhile, a group of about 10 British people, including the McCanns and their friends, have been reinterviewed to clarify their statements.
They are expected to record video evidence in court this week for any future trial.
Local lawyer Artur Rego said the procedure was only used in exceptional circumstances when a large number of witnesses were foreigners.
On Sunday, Madeleine's grandmother Susan Healy made an appeal for the return of her granddaughter.
She told BBC News people should look out for her granddaughter's distinctive "black flash" in her eye, where her pupil runs into her iris.
"If the people who have got Madeleine realise that she has this distinctive marking, take her somewhere safe. Leave her, you can run off, we don't care whether you get caught, that doesn't matter. We just want Madeleine back," she said.
Tributes in pictures
Businessman Sir Richard Branson, footballer Wayne Rooney and children's author JK Rowling are among those who have contributed to rewards totalling £2.5m for the safe return of Madeleine.
The official ground search for Madeleine in the Algarve has ended, but police say they still have significant leads to follow up.
They have formally interviewed a 12th person as part of their investigations, but say no individual is being considered a suspect.
The focus has shifted from a local search for Madeleine to an international child abduction inquiry, amid suggestions she may have been taken out of Portugal.
Detectives are also continuing to cross-check CCTV footage of several cars with witness statements in their efforts to identify a possible abductor.
Police have declined to confirm or deny reports about any possible leads, citing Portuguese law.
The international number for Crime stoppers is +44 1883 731 336. People with information about Madeleine can call anonymously.
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