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''All we need is a clue to move the search forward, we need the public's help,'' Christopher's father, John Bates, said.
Yesterday marked five months since Christopher was last seen.
''We would like to say thank you to everybody that's helped look for him and [tried to] bring him home,'' Mr Bates said.
''Chris's friends who have come up to search ... the food brought to our house ... we're very privileged to live in an area where people are so generous.
''Week in, week out the LandSAR guys have given literally thousands of man hours to help bring Chris home, and thank you to the police for everything they've done to date.''
Acting Central Otago sub-area supervisor Detective Sergeant Derek Shaw said no physical search had been made for eight weeks.
The overall search was still ongoing and had been concentrated east of Alexandra.
The next step would be a more thorough test of mobile phone data records that could link to Christopher's phone, Dec Sgt Shaw said.
Asked how he would evaluate the search, Dec Sgt Shaw acknowledged the work of volunteers.
''We haven't found him, that does concern you because you want to do the best you can for Chris and his family, so that doesn't sit easy with me, but when you look at the dedication of the LandSAR volunteers ... they must have done close to 1000 hours - there's been an immense effort put in.''