Dog walkers and farmers were asked today to join the hunt for missing teacher Jane Longhurst.
Police are treating her disappearance as murder and they want people to be vigilant and report any unusual sitings in woods or fields.
Officers are carrying out selective searches but Detective Inspector Chris Standard, second-in-command of the investigation, said members of the public could help.
He said: "We are asking farmers throughout Sussex to check their land and outbuildings.
"Dog walkers all over Sussex can assist by keeping their eyes open.
"If anyone sees anything suspicious, they should call the police and not disturb anything."
Mr Standard appeared on GMTV yesterday with Miss Longhurst's partner Malcolm Sentance, her mother Liz and sister Sue, to appeal for information.
Her family is convinced Miss Longhurst would not have walked away from her life.
The 31-year-old music teacher disappeared from her home in Shaftesbury Road, Brighton, three weeks ago tomorrow and detectives fear she has been abducted and murdered.
Miss Longhurst, who teaches at Uplands School for children with learning difficulties in Hollingdean, Brighton, was last seen at 2.40pm, on March 14, entering her home and carrying shopping bags.
Mr Sentance returned home just after 4pm and there was no sign of her or evidence of a struggle. Her shopping was also missing.
She was carrying her mobile phone, a Next bag, purse and keys.
Her family lives in Reading and police may put up appeal posters at the Reading v Brighton football match tonight.
Anyone with information should contact the Operation Keen incident room at Brighton police station on 0845 6070 999.
Phil Mills
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