Chinese national Tingjun Cao, 53, has been accused of her kidnapping and murder. Cao is set to go on trial in October.
Detective Inspector Nicola Reeves said on Tuesday the current search in Greenpark involves a team of more than 60 people.
Police are focussing on farmland near the intersection of Hudson Rd and Clarks Rd.
The area has been searched before, but new information relating to the case has prompted investigators to return to the location.
Reeves said police are acting on the leads and information they receive.
"We are still determined to do everything we can to find Yanfei and we continue to follow up information that might lead us to her whereabouts.
"We would like to thank the farm owners in this area who have allowed us to return to search again, and who have been so cooperative with us throughout our efforts."
With RNZ
