"Playing drinking games- and it sure wasn't Just Juice in those cups- supports a youth drinking culture that is a severe problem here in New Zealand. Binge drinking and alcohol abuse are not to be taken lightly, and my friends terrify me with their irresponsible consumption. For a political candidate to actively support such a thing is utterly appalling."
Another person at the party said there were teenagers aged 17 at the residence drinking alcohol.
But today the politician said the party was one way of reaching out to youth on their terms.
Seymour, who is considered a meme and lovable larrikin to many young people, had been to a campaign "Drinks with David" event at Mission Bay prior to turning up to the house party.
Seymour told the Herald he spent around 20 minutes at the party where he played beer pong and won. He also took the opportunity to tell everyone present to vote for the Act Party.
"If you can squeeze in meeting another 10-20 voters at the end of an 18 hour day, if that's not good campaigning I don't know what is."
He dismissed concerns of underage drinking and criticism of appearing to endorse a youth drinking culture saying the party appeared well supervised and orderly. He was also vigilant to tell those on social media to be safe when consuming alcohol.
Seymour said turning up at the party also connected him with youth in their own environment.
"It's a bit of a paradox. People worry about politicians being unapproachable and the youth being disengaged. I work hard to engage with younger voters and I think going to their setting is a positive thing."