"This brazen daylight attack was very distressing and frightening for the victim," Ms Gillespie said.
"We need to identify this offender as soon as possible so we can ensure he does not have the opportunity to do this to anyone else."
The man was described as about 20, of Maori descent, about 167cm tall with short black hair and of medium to solid build. He was wearing a grey T-shirt over his face and had a Maori design tattoo on his left arm.
Police were interested to hear from anyone who saw any suspicious activity in the area of Kirks Bush and the surrounding roads, particularly anyone who may match the description of the offender, Ms Gillespie said.
Police advised people walking through the park to have somebody accompany them, and to keep their cellphone where it could be reached.
"Dial 111 immediately if you see any suspicious activity in a park," Ms Gillespie said.
"Anyone who may have seen anything suspicious between 3.30pm and 4.30pm on Tuesday, 25 November in the area of Great South Road, Beach Road and Settlement Road which surrounds Kirks Bush, should contact police."
People with information could call Ms Gillespie on (09) 295 0345, or anonymously to Crimestoppers on 0800 555 111.
