Balloons are being released all over the world, to mark the 50th day since Madeleine McCann went missing.
The McCanns say the aim is to ensure Madeleine is not forgotten
Yellow balloons are being freed in 50 countries to raise awareness of the campaign to find the four-year-old.
Parents Gerry and Kate McCann took part in an event on the beach at Praia De Luz in Portugal, the resort from which Madeleine went missing on 3 May.
The McCanns have also written an open letter thanking the British media for its support in the hunt for Madeleine.
Similar balloon releases were planned by supporters in countries including Argentina, the US and Australia.
In Dublin, 50 yellow and white balloons, displaying contact details for people with information to call, were released by local schoolchildren.
In Afghanistan, campaigners will fly 50 kites emblazoned with pictures of the missing girl, a report on the FindMadeleine website said.
And in California, 50 white doves will be released.
A small ceremony has also been held at Glenfield Hospital, where Mr McCann works.
On behalf of his colleagues, the Reverend Maggie Sharp said a prayer for Madeleine.
"The abduction of Madeleine has hit us really hard, it's opened our hearts and minds to another kind of suffering and another kind of agony.
"We come together to say we are not going to forget, we are going to go on supporting."
A message from the McCanns on the website said: "The objective is simple - after seven weeks missing, we must continue to ensure she is not forgotten."
Madeleine's parents are also considering releasing a cover version of the Bryan Adams song Everything I Do, I Do It For You, in an effort to raise more money for their campaign.
Speaking to Sky News, Mr McCann said: "That song, at the minute, best reflects how Kate and I feel emotionally and how determined we are to continue searching for Madeleine."
In their letter, the McCanns express their "deep gratitude" to British news organisations, and ask the media not to carry any more pictures of their twins, Sean and Amelie.
The couple also say that the balloon release marks a new, "event-driven" phase of their campaign.
Earlier, police in Malta said they are investigating possible sightings of Madeleine McCann.
A number of UK tourists have reported seeing a child resembling the missing four-year-old in the island's capital, Valletta, and the resort of Sliema.
One said he saw a couple with a girl, who appeared to be wearing a black wig.
A spokesman for Madeleine's parents, Gerry and Kate McCann, said they were not giving credence to the claims at this stage.
Maltese newspaper In-Nazzjon reported that two tourists told police they had seen a girl matching Madeleine's description in Valletta.
And Ray Roberts, from Anglesey, north Wales, said he saw a child in Sliema wearing what looked like a black wig and being told "Get up, little girl" by a man of Arab appearance.
"The more I think about what I saw the more convinced I become that it may well have been Maddie," he said.
The McCanns' spokeswoman said they were not focusing on the sightings until more information was available from an official source.