After her win on Saturday, social media users pointed out the repeated use of a racial slur in what appeared to be her personal Twitter account in 2013 and 2014.
Users posted screen grabs from what appeared to be an account with her name and photo
with several references to the slur.
The authenticity of that Twitter account could not be verified and the tweets from that account are now private.
Hay, 18, responded to the allegations online, but did not apologize directly in reference to the alleged use of the word.
"Several years ago, I had many personal struggles and found myself in a place that is not representative of who I am as a person," the statement read in both her Instagram and Twitter accounts.
"I admit that I have used language publicly in the past which I am not proud of and that there is no excuse for. Through hard work, education and thanks in large part to the sisterhood that I have come to know through pageants, I am proud to say that I am today a better person.
"I am honored to hold this title and I will use this platform to promote the values of The Miss Universe Organization, and my own, that recognize the confidence, beauty and perseverance of all women."
Despite questions of Hay's character and calls for her to be stripped of her crown, Miss Teen USA appeared to stand by its latest winner.
The Miss Universe Organization, which oversees Miss Teen USA, issued a statement saying that "As Karlie stated, she was in a different place in her life and made a serious mistake she regrets and for which she sincerely apologizes."
The statement, obtained by KTRK, a CNN affiliate in Houston,
near her hometown of Tomball, read: "The language Karlie Hay used is unacceptable at any age and in no way reflects the values of the Miss Universe Organization." After condemning her language, it concluded that it was "committed to supporting her continued growth."
Pageant was already being criticized
Critics left scathing comments on social media accounts accusing the organization of trivializing the racial slur.
CNN attempted to reach both Hay and the Miss Universe Organization.
Miss Teen USA seeks women who are "savvy, goal-oriented and aware," according to its website.
Hay graduated from Tomball High School this year and "hopes to enroll at Texas A&M University." She aspires to be a businesswoman and wants to advocate for people affected by drug and alcohol abuse, according to her pageant profile.
Kamie Crawford, a former Miss Teen USA, tweeted some advice: "If u win any pageant - first things first. Clean up ur page."
The pageant had already come under some criticism over the lack of diversity. The top five contestants for the title were fair, blonde women, which had Chrissy Teigen jokingly tweeting
: "Wow how can we choose from such a diverse bunch."