"Not like this," he said.
"Sometimes she goes over to a beach on the North Shore, but I was over there yesterday and I didn't see her."
Tyler Avison said he had been flooded with messages from friends of his younger sister.
"They've all been messaging me and saying that if they see her they'll let me know... and they keep asking."
His sister was leaving for her job at Auckland Transport on Thursday morning, but she was leaving later than usual.
She was often at Muriwai Beach, but he unsuccessfully searched the area for her yesterday.
Tyler Avison said the pair were close, and her disappearance was deeply worrying.
He was determined to continue searching for Carissa.
"That's all I can really do."
Police refused to be drawn this morning on whether they suspected foul play had anything to do with her disappearance.
Friends and family have shared photos of her on social media in the hope of gaining details about her whereabouts.
A family member posted on Facebook that they were "desperate" to find her.
"We would be so grateful for any clues," the post read.
The alarm was raised after she failed to show up for work, which is out of character for her.
Carissa is of slim to medium build and has a Japanese scripture tattoo on her left forearm.
She has contacts in Papamoa, Southland and the wider Auckland region, but is not known to have access to a vehicle.
Police want anyone who may have seen Carissa or has any information about where she might be to call them on (09) 302 6400 or anonymously contact Crimestoppers on 0800 555 111.