Kate McCann, who broke down in tears at the end of her impassioned plea, asked viewers to have courage to come forward with information on her daughter Madeleine. Madeleine went missing on the southern coast of Portugal during a family summer holiday.
"Please help us," she told Spain's Antena 3 television channel in an interview recorded in Britain Tuesday. "Find it in yourself to have that courage to make that call.
CBS News correspondent Richard Roth reports this was a plea for public vigilance - in the hope that someone in southern Europe or North Africa may still have information that can help them find their daughter.
"It's a long time to be without Madeleine. I strongly believe that Madeleine is out there," the toddler's mother said.
"I think she's probably in someone's house, I don't know why. I suppose it's a feeling but I feel, as Madeleine's mummy, I feel in my heart really that she's there. I don't believe Madeleine has been taken away from us permanently."
Her husband Gerry McCann said suggestions they may have given drugs to their daughter to sedate her were outrageous.
Some media reports have indicated Portuguese police suspect Madeleine's parents may have accidentally given her an overdose of sedatives before they went out to dinner with friends, then disposed of her body. Gerry and Kate McCann have repeatedly dismissed the suggestion.
"It's ludicrous. These sort of questions and the publishing of them are nonsense, and we shouldn't be giving them the time of day. There is absolutely no suggestion the children were drugged, and it's outrageous," he said.
Portuguese police have declined to comment because Portugal's secrecy laws forbid detectives from speaking about ongoing investigations.
Madeleine McCann went missing on May 3, a few days before her fourth birthday, from her family's hotel room during a vacation in Portugal's Algarve region.
After initially focusing on the possibility that she was abducted from her hotel room, police switched their focus to her parents when forensic tests conducted at a government laboratory in Britain found evidence that DNA from Madeleine was in the trunk of a rental car the parents used after her disappearance.
"There is nothing in those DNA tests related to Kate and I that will show anything other than completely innocence," Gerry McCann said. "I'm confident of that, because we have done nothing."
Police named the parents as formal suspects. They have returned to their home in Britain.