The caller said 23-year-old Guildford had been in the area for some time and had been seen in Ohakune township.
The former Hawke's Bay player, who shot into prominence with the 2009 World Cup winning New Zealand Under 20 side, is on indefinite leave from the Crusaders as he seeks treatment for his drinking problems, sparked by an incident in Christchurch last month that saw the former All Black allegedly assault another man.
Doubt remains over his rugby future in New Zealand, though it is understood that the NZ Rugby Union could be ready to offer him a lifeline on the back of his current treatment.
Guildford is in the midst of a one-month course of "intensive" treatment at an undisclosed North Island location.
The Chronicle contacted his agent, Simon Porter, but he refused to confirm where his client was receiving treatment.
"We said all we are going to say about Zac's treatment plan in a press release a few weeks ago," Porter said.
That release did not identify where the player would be getting his treatment.
Neil Sorensen, NZRU general manager professional rugby, said the union was not going to make any comment.
Ahuru Recovery Retreat is a plush lodge at Karioi, between Waiouru and Ohakune in the shadow of Mt Ruapehu. Its website says it provides world-class treatment programmes "for the support of clients whose desire is to have an alcohol and drug-free life".
A person attending the retreat's programme would be one of a few clients receiving treatment at any one time. But it comes at a price. Its programme prices range between $19,995 and $22,995.
The lodge offers a 28-day programme including intensive therapeutic intervention, activities, one-on-one counselling support, and a full psycho-educational recovery programme.
There are also weekly excursions, all meals for the four-week period and a structured follow-up plan.
The website said a typical day includes physical activity, "self-directed reflection and writing", group discussions and individual counselling.
But while stopping the use of alcohol and drugs was important, Lodge has
rich history
the lodge promotional material said "it is just the beginning".
"The focus is on developing the skills necessary to recognise and manage underlying vulnerabilities without the need for alcohol ... thus establishing the foundation for an entire lifetime of freedom".
Don Graham is the clinical director at Ahuru. He has worked at Hanmer Clinic and with Waitemata Health, treating clients with alcohol and drug addictions.
The lodge has been in the news before: it was built as luxury accommodation with $500,000 stolen by a former IHC fundraising manager, Lynn Fiebig, who in 2010 was sentenced to three years' jail for the theft.
It was sold the same year and converted into a residential rehab facility.