Johnny Sleigh (36), described yesterday by sister Catherine Booth, of Timaru, as a "typical Kiwi bloke", failed to return home after leaving a nightclub early on Saturday.
Concerns were raised on Monday by friends after he did not return messages left on his phone and did not turn up for work.
Mr Sleigh is the son of Peter and Caroline Sleigh, who farm near Waimate.
Mrs Booth said they had been in regular contact with London Metropolitan police, who have mounted a major investigation into Mr Sleigh's disappearance.
Three close friends have taken time off work to conduct their own search, distributing fliers appealing for information and contacting people they hope may know where Mr Sleigh is.
The family had received no further information yesterday about where he might be or what had happened.
Police had obtained CCTV footage from the nightclub which showed Mr Sleigh leaving about 1.20am last Saturday.
"He left by himself, he was walking all right and did not appear drunk or anything.
"He was then seen walking off down the road towards Oxford Circus where he would have been able to catch a bus to go home," Mrs Booth said.
The family was keeping in close contact with London police and Mr Sleigh's friends. At this stage, family members were not planning to go to London.
"Police have told us there is nothing we can do over there. They are doing everything they can and close friends are undertaking their own search and inquiries," she said.
Since being notified Mr Sleigh was missing, the family had been "pretty up and down".
"We are hopeful and then at other times not so hopeful," Mrs Booth said.
Mrs Booth said his interests revolved around the outdoors. He enjoyed snowboarding and running, and had competed in marathons in Berlin and Iceland.
Mr Sleigh, who had been in London for six years, maintained "fairly regular contact" with his parents and four brothers and sisters.
Police had checked his bank account and the last withdrawal had been on the Friday night.
Mrs Booth said the family wanted anyone with any information to contact London's missing persons unit or New Zealand police.
