Madeleine McCann's dad Gerry said 'every parent loses a child' as he launched a mobile phone rescue alert for missing children.
More than seven years after his daughter went missing, Gerry McCann, 46, said even losing a child for a moment was intolerable.
He said: "Every parent has lost their child, even if it is momentarily - in a playground, in a supermarket - and knows how terrifying it is."
He and Madeleine's mum Kate appealed for parents to download the new Child Rescue Alert smart phone app.
Gerry added: "I'm sure it would have increased the chances of finding Madeleine."
The couple were joined by Hugh Grant and parents of other lost children for their plea to the public to back the scheme.
Kate, an ambassador for Missing People, said: "People are a crucial resource and are very willing as we know from our own experience."
Speaking on ITV's Good Morning Britain, she added: "The Child Rescue Alert is based on the Amber Alert System in America - already 685 children have been reunited with their families so we know it works."
Coral Jones, mother of murdered five year old April, said: "If we had all this before we would have had more of a chance of having April home."
Hugh Grant added: "To let everyone in the country know that this child is missing, with a photograph, could mean the difference between life and death.
"The first hour or two is crucial and it is a good function for a smart phone. It is a brilliant idea."
National Crime Agency figures reveal a child is reported missing in the UK every five minutes. From 2012 to 2013 there were 306,000 reports of missing people.
The dedicated app sends out alerts as soon as a child disappears. So far 58,000 people across the country have signed up to the scheme.
Missing People's Chief Executive Jo Youle said: "If your child goes missing you want the whole world to stop and search. The Child Rescue Alert enables members of the public to receive the alerts for vulnerable and high risk missing people straight to their phone and they can help get that child back very quickly.
You can register atChildrescuealert.org.uk.
Madeleine was three years old when she disappeared in Portugal's Praia da Luz in May 2007 while her parents were dining nearby with friends.