Elgort wrote that he was "distressed" to see the claims about his behaviour on social media.
"I cannot claim to understand Gabby's feelings but her description of events is not what happened."
However, the star did admit to his "relationship" with Gabby not ending well and apologised for how he acted.
"I stopped responding to her, which is an immature and cruel thing to do to someone," he wrote.
"As I look back on my attitude I am disgusted and deeply ashamed of the way I acted."
Gabby has appeared to have deactivated her Twitter account since posting her story on social media. Her post contained distressing details of the encounter.
She claimed that she told Elgort she was soon turning 17 when he shared his private Snapchat account with her. She also alleged that the actor shared nude photos of himself with her and shared screenshots of their messages to Twitter.
The young woman also alleged the actor asked her for a threesome along with one of her dancer friends who was "as well underage". She claimed she didn't tell anyone because Elgort told her it could "ruin his career".
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.
If you're in danger now:
• Phone the police on 111 or ask neighbours or friends to ring for you.
• Run outside and head for where there are other people.
• Scream for help so that your neighbours can hear you.
• Take the children with you.
• Don't stop to get anything else.
• If you are being abused, remember it's not your fault. Violence is never okay.
Where to go for help or more information:
• Women's Refuge: Free national crisis line operates 24/7 - 0800 refuge or 0800 733 843 www.womensrefuge.org.nz
• Shine, free national helpline 9am-11pm every day - 0508 744 633 www.2shine.org.nz
• It's Not Ok: Information line 0800 456 450 www.areyouok.org.nz
• Shakti: Providing specialist cultural services for African, Asian and Middle Eastern women and their children. Crisis line 24/7 0800 742 584
• Ministry of Justice: www.justice.govt.nz/family-justice/domestic-violence
• National Network of Stopping Violence: www.nnsvs.org.nz
• White Ribbon: Aiming to eliminate men's violence towards women, focusing this year on sexual violence and the issue of consent. http://www.whiteribbon.org.nz
