Goetze came off the substitutes bench to score a stunning 113th-minute goal as Germany beat Argentina 1-0 at Rio de Janeiro's Maracana Stadium.
"I told Mario Goetze, 'go out and show the world you are better than Messi'," said Loew.
"Goetze is the miracle boy, he is the wonder who can play in numerous positions, he is the decider who can come on and make a difference and that is what he did today."
It came after four consecutive near-misses in major tournaments stretching back to 2006.
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"We have been together for 55 days, we have started this project years ago and this is the culmination of a lot of hard work," Loew said.
"We have been able to improve our performances, we believed in it and worked a lot for it. This team really deserves it with the likes of Philipp Lahm, Bastian Schweinsteiger, Lukas Podolski and Per Mertesacker.
"We have had disappointment in the past having gone close despite playing good football. I think we put in the best performances over all the seven matches of all the teams here."
"This team has developed an unbelievable team spirit and has developed a marvellous mental capacity," he said.
"And we are proud to become the first European country to win the title in south America. In Brazil, In Rio is this football-loving country and that makes us very proud."
"This deep joy and happiness will last forever, the team gave all they had lead by the marvellous Bastian Schweinsteiger in midfield and Philipp Lahm, who ran a number of kilometres.
"I told the team before kick-off that they would have to give more than they had ever given before, because they wanted to achieve something we had never previously achieved.