Last year 10,000 people turned up, which has replaced the Mardi Gras at the Soundshell.
She said Thomas would perform an extensive set with a backing band in the second half of the show, including her No1 hit single, It's Worth It.
The 22-year-old captured the hearts of New Zealanders during the first season of X Factor, with her self-titled album reaching gold status.
Patuwai will also perform some of the hits he took to the X Factor stage, including his debut single Something Special.
"Both artists will be joined by a number of talented performers including Whakatane's Cameron Rota, who also auditioned for X Factor and was placed in a new boy-band group, TYP: The Young Project."
The group made it to the top 14 of the competition.
"The Party in the Park event will start at 6pm and finish with an earlier fireworks display at 9pm, allowing children and their families to be a part of the New Year's festivities. This will be followed up with an exciting fireworks display at midnight."
She said they had taken notice of feedback from last year, including the need for more shade. Ms Lang said the main point of difference with Rotorua's GLO Festival was that the New Year celebrations were held over several days, not just on New Year's Eve.
"Rotorua is a vibrant family-friendly destination, so there are a number of different events and opportunities to celebrate the festive season."
Other GLO events include the First Big Brunch on New Year's Day, where families are invited to bring a picnic and enjoy the free live music at the Village Green. This is followed by the final event, the Summer Fiesta at the Rotorua Night Market on January 2.
"Rotorua is becoming nationally-renowned for its night market, and its special event themed markets are particularly popular. The Summer Fiesta will continue that trend."
Full details can be found at www.rotoruaglofestival.co.nz.