Guarin had reportedly agreed terms with Juve on Tuesday while Vucinic had passed a medical with Inter in what looked to be a done deal.
However, a section of Inter fans were opposed to the move and demonstrated outside the club's headquarters on Tuesday before Thohir ended all negotiations.
Thohir said on the club's official website, www.inter.it: "After speaking to my closest aides and exchanging views with Massimo Moratti and his son Angelomario this morning, I decided not to continue negotiations with Juventus.
"I felt it was not possible to reach an agreement on a deal in which the opinions of the two parties differed and which did not offer a clear financial or technical benefit to the club.
"As was said in the recent club statement, I have already asked our sporting directors to evaluate other transfer opportunities that will enable us to strengthen the team in line with the financial parameters imposed by Financial Fair Play.
"Again, I believe we must all remain united, the fans, the club and the team so that we can get back to the standing we all want for this club and that Inter deserves."
Inter have struggled in front of goal in 2014 and are looking to strengthen their attacking line in the winter transfer market.