On Tuesday, after a less-than-stellar debate performance, Donald Trump returned to using one of his favorite measurements to mask his missteps on Monday night — the polls.
Except that the post-debate "polls" the GOP nominee and campaign kept touting that he won on social media, at his rally in Florida and in press releases aren't polls at all. They're essentially unscientific Internet popularity contests, are not weighted as to what the electorate will actually look like, and have no predictive value. In fact, if you're worried about voter fraud, in many of these surveys people can vote multiple times and they can easily be rigged by Internet bots.
Many of the results he cited came from very Trump-friendly sites, such as Breitbart News and the Drudge Report. Some of these polls were shared by Trump supporters on reddit, encouraging people to go vote. These were not selective samples with any merit, and in no way could they accurately measure whether the more than 81 million people who tuned in for the debate thought Trump did better than Hillary Clinton.
http://www.npr.org/2016/09/28/495805190/no-donald-trump-didnt-win-post-debate-polls
