the reports of a child being seen on thursday night are just that, reports and nothing more. they've come from local journalists who claim to have sources close to the police, but the police have not confirmed anything, neither have they confirmed that it is a brittish person. Someone said on midday news on five live just now "this happened on thursday night, and since then there have been hundreds of phonecalls, and hundreds of little girls have been seen, but it doesn't necessarily mean that they were madeleine".
I think that in a case like this people seem to have this need for knowledge, and in the absence of formal confirmation of what is going on, the media grasp at snippets of information and, to a certain extent, make up the details as they go along. "police are investigating whether it could be a brittish person" well they would be. portugal has a huge expat community, so the idea that it could be a brittish person is not beyond the relms of possibility. "police are investigating reports of a man seen dragging a child towards a marina on thursday night", someone might have seen it. it could have been some rich boat owner dragging his stroppy, tantruming toddler towards his boat, or could have been someone trying to carry their drunk partner back home to their villa close to the marina, but if seen late at night, and with a bit of imagination, it could be imagined that it was a child, you know, someone could think "child gone missing, wait a minute, I saw some bloke dragging someone towards the marina on thursday ... could have been a child ... come to think of it they did look small and helpless ..." and then they get on to the phone to the police, or the media, and before you know it police are "investigating". and especially when continued appeals are put out "if you saw anything, however insignifficant", people will think and think whether they saw anything and might remember the smallest amount of detail..