Miss King said it was horrible someone had stolen her painting.
"It's a real shame as it was donated via the competition for the hospital's benefit, along with the other artworks. Hopefully the person who took it will have second thoughts and it will be returned."
The Transfusion Art competition gives Year 12 and 13 art students across the region a chance to donate their work to Waikato hospitals, while competing with their peers.
The works are exhibited and judged at Waikato Museum before being displayed indefinitely at the hospital.
Hamilton Boys' High School head of art James Sutherland, who helped set up the contest, said the news was disappointing.
"It's lamentable that people would take the artworks off the wall considering the purpose of them is to bring a little bit of sunshine into an otherwise dull environment."
He said the stolen piece was a "stunning bit of painting for the [age] level".
Mr Sutherland said it was difficult to put a monetary value on the painting, which was the second to go missing since the competition was launched in 2009.
If the students went on to become successful artists the works could become valuable, he said.
Waikato District Health Board arts advisory committee chairwoman Mary Anne Gill said the painting was valued for what it did for patients, visitors and staff.
"The impact it could have had on grieving people means it is worth a fortune, but not in monetary terms."
Mrs Gill said the piece had recently been selected by art historian Tim Walker to hang in the waiting room of the new morgue.
"He said it had the ability to calm people when in a distressed state."
Hospital security were checking CCTV footage for clues.
Mrs Gill said if the art was handed in, no questions would be asked.
