But, in spite of a huge international police operation, there are still no real leads on what might have happened to Madeleine, according to CBS News correspondent Elizabeth Palmer.
Over the years, there have been hundreds of supposed sightings of Madeleine, but not one of them has panned out. Her parents, Kate and Gerry McCann, still hope she'll one day be found alive and have released a new video to mark the anniversary.
The video's focus is the McCanns' search for their daughter. Palmer says the family has long been handing out posters and photos, combing the Internet, and responding to tips from the public.
The couple has also spoken out in an interview on Portuguese TV about what they observed the night Madeleine was last seen.
Kate McCann said, "The shutters, which had been down all week, when I went in and there was the gust that blew the curtains open, that's when I noticed that the shutter had been pulled up."
On the night of May 3, 2007, the McCanns left their three children sleeping in the family's vacation condo, and went to dinner at a restaurant 100 yards away.
Around 10:00 p.m., when Kate McCann went to check on the children, she found Madeleine was gone.
The McCanns have dismissed a theory that she wandered off. They are convinced she was abducted.
Gerry said in the recently released video, "If you're saying is it theoretically possible that Madeleine left the apartment? Then yes. Do we believe it -- and do we believe she was capable of leaving the apartment the way it was found -- then I would say absolutely not."
Since 2007, several photos of Madeleine have been widely publicized. One shows her distinctive right eye, and another is a projection of how she might look two years on.
The McCanns say they will ask the Portuguese police to re-open the investigation into Madeline's disappearance to follow up what they say are new leads uncovered by private investigators hired by the McCann family.
Pat Brown, a criminal profiler, said on "The Early Show" Monday that a combination of factors has contributed to where things stand in the McCann case.
"(One theory) was that the child was abducted. And another theory was that she died in the apartment, and this, of course, is the theory the McCanns aren't too happy about. And they don't want that one out there," Brown said.
"And so they're still angry at the Portuguese police. And this is one thing I don't think they should bring up at this point in time. After three years when they're looking to get the cooperation of the police, it's not the time to say, 'You're not following up our leads.' And they also mentioned that it's possible they aren't following up the leads because they don't want the child to be found alive, because that would be embarrassing. Not what you want to say. You want to keep it positive and ask for somebody's help and not bring anything negative into the conversation."
As for the McCanns' supposed leads, Brown said she hasn't heard of any actually getting anywhere.
"Ever since the very beginning, when they have believed that the private investigators had great leads that weren't being followed up on, I never saw that they panned out to be anything. And they're saying that there's other leads that aren't being followed up, and I don't know what those are, and I don't think anybody really does. I don't know what leads they could be finding at this point in time."
Brown added, if the McCanns are innocent of any wrongdoing, they will continue to search for Madeleine.
"They're always going to believe their child is out there. That would be normal for any parent whose child has gone missing. They're not going to give up on her. So they're doing the right thing in the sense that they're trying to keep her in the public eye."
However, Brown added, "Quite frankly, this child has been seen everywhere. I mean, as far as missing children go, she's one of the most publicized missing children in the world. So that's one of the most unusual things about this: With her picture out as much as it's been out there, she would have to be pretty well hidden for her not to have shown up at this point."
If you have information on Madeleine McCann's disappearance, visit Find Madeleine.com.