Williams extended the school's "deepest condolences" to her family and friends.
Nathan was a student at Tāmaki College.
A friend of Ella, Georgia Wilson, posted on Instagram: "For those of you who don't know or are unsure, Yes my best friend Ella is gone, she past in a car accident early this morning. I would like to thank everyone for sending love to this gorgeous girl she would be so thankful. Rest easy I love you so much xx.
"You were the only person I could be myself around and talk to about everything and cry to you when I need you and hug when I need a hug and no matter what we would always be there for each other. And now your not here so I have no one I can tell everything. I'm just in so much shock I still can't believe that your gone," Georgia wrote.
A friend of Nathan, Cam Bryson, posted: "Rip Nathan you left too soon hope your in a better place and can't wait to ride with you again one day."
Police said speed appeared to be a factor in the crash in which the teenagers' car slammed into a building in Pakuranga Rd about 4.30am yesterday.
A bunch of flowers marked the scene of the crash by yesterday afternoon.
A patch of torn up grass marked where the car appeared to have come off the road.
Two street lights had been knocked over and a fence on the side of Pakuranga Rd was crumpled and partially ripped off.
Police want to hear from anyone who saw a dark-coloured Honda Accord near Pakuranga Rd about 4.30am.
Anyone with any information is asked to contact Counties Manukau Serious Crash Unit on 09 261 1300.