I'm not sure about that.
So many Portuguese appear to have been brainwashed by the tabloid media (rags and TV matinée shows) and by pro-Amaral supporters. I doubt that that many of them even continue to follow the case - they've decided that she's dead (after all the former lead investigator assures them of that every time he gets air space)... and life moves on.
Those on the saner end of the sceptic scale who continue to follow the case in English-speaking media no doubt would quietly report a sighting. At least, I would hope so.
I'm not too convinced whether those on the mentally wobbly end of the sceptic spectrum would, even if she knocked on their doorbell.
I'm sure each of us has seen young girls who for a second you think look like Madeleine, but it's the Madeleine of eight years ago. That's a more likely reason why someone might not report it, they just know it's extremely unlikely.
Some people clearly do still report these sightings though, as a newspaper report in this thread indicates.
But I wasn't thinking about sightings, but about someone stumbling across non-visual evidence - hearing something or seeing other evidence. In those cases we'd all report it because you wouldn't know when you stumbled upon evidence of a child being held or mistreated who the child is, and so the rational side of your brain wouldn't intervene to tell you to get a grip.