(Adds company comment on Marciano denying allegations and details on previous allegations against Marciano)
Feb 1 (Reuters) - Guess Inc shares fell more than 17 percent on Thursday following a tweet by model and actress Kate Upton accusing the company's co-founder of using his power to harass women.
"It's disappointing that such an iconic women's brand zGUESS is still empowering Paul Marciano as their creative director
#metoo," the model tweeted on Wednesday, using a popular hashtag designed to highlight the wide spread of sexual harassment.
"He shouldn't be allowed to use his power in the industry to sexually and emotionally harass women #metoo," Upton tweeted, without elaborating.
A representative for Upton, who modeled for Guess in 2011, did not respond to requests for comment on Thursday.
"Mr. Marciano denies any misconduct toward Ms. Upton," Guess said in a filing with the U.S. Securities and Exchange Commission on Thursday.
The fashion retailer said it will investigate Upton's concerns if it determines they have merit, adding that she had not yet made any specific allegations.
Guess also said it had investigated claims that Marciano behaved inappropriately towards two women in November 2017, after an entertainment website contacted them.
It said the investigation, aided by outside counsel, had so far been unable to corroborate the allegations and the company's board had been unable to determine if they had merit. Marciano has denied the allegations.
Marciano separately responded to Upton's allegations through celebrity news website TMZ, saying he never touched Upton, and has never been alone with her. He said he would not apologize as he had done nothing wrong, TMZ reported.
"If she has a claim, there's one place to tell the truth and thats in court or to the police," he told TMZ.
Marciano could not be reached by Reuters for comment.
Guess shares ended down 17.7 percent at $15.11 on Thursday, wiping more than $250 million off the company's market value. (Reporting by Uday Sampath, Nandita Bose and Bernie Woodall; Editing by Bill Rigby)