Kate and Gerry McCann are determined to do everything necessary to search for their daughter
A retired British solicitor, Tony Bennett, has set up a fund called The Madeleine Foundation, which aims to bring a private prosecution against the McCanns for alleged child neglect.
But Madeleine's parents fear members of the public will inadvertently donate money to it because they may mistake it for the McCanns' own Madeleine Fund, which pays for private investigations into her whereabouts.
Mr Bennett, 60, who has in the past worked with the family of Stuart Lubbock, the man found dead in Michael Barrymore's swimming pool in 2001, described his fund as a subscription-only members' club, charging a £10 annual fee.
Last year he tried unsuccessfully to launch a private prosecution against the McCanns, only to be told by magistrates in Leicester that they had no jurisdiction over the case, because Madeleine disappeared in Portugal.
Mr Bennett said: "Some of the money immediately raised will be used to pay for a barrister to give his or her opinion on how best to proceed with a legal action against the McCanns.
"We are a group of people, which is rapidly growing in number, who want to get to the truth of what happened to Madeleine.
"We will also campaign for changes to the law about parents who leave children on their own.
"If you go on the internet and look at some of the forums and blogs about Madeleine, there is a large and significant number of people who feel powerless and who want to do something about it."
Mr Bennett said the official website for the Madeleine Foundation, which will not have charitable status, is about to go live.
He said all the money raised would be used "in an above board way" and would be openly accounted for.
Clarence Mitchell, the McCanns' spokesman, said: "It is a great shame that Mr Bennett feels the need to make money out of Madeleine McCann. "He did not seek permission from Gerry or Kate to use Madeleine's name. This so-called foundation is in no way doing anything to help find Madeleine.
"It purports to be a foundation helping the search for Madeleine but it does nothing at all to help that search and goes against Gerry and Kate.
"Mr Bennett has already tried to take a private prosecution against Gerry and Kate but a court said it has no jurisdiction over something which allegedly happened in Portugal."