Helen Bailey, who wrote the Electra Brown series, was last seen walking her dog near her home in Royston, Hertfordshire, on 11 April.
There has not been any trace of the 51-year-old or her pet despite searches.
Her partner Ian Stewart said: "Whatever has happened, wherever you are I will come and get you."
Read more on this story and others from across Hertfordshire
Northumberland-born Ms Bailey, who lived with her partner, had gone for a walk with her miniature dachshund Boris and had reportedly said she "needed a little time to herself". She was reported missing on 15 April.
As well as the teenage book series, she started a blog called Planet Grief after her husband of 22 years drowned on holiday in Barbados in 2011.
Officers searching for the author have carried out extensive searches of the local area and checked hundreds of hours of CCTV footage. They have said there is nothing to indicate "foul play"".
In a statement, Mr Stewart said he hoped she would hear his message and "listen carefully".
"We miss you and Boris so much... We are shattered in so many ways," he said.
"You not only mended my heart five years ago but made it bigger, stronger and kinder.
"Together we learnt to live with our grief and move forward with our lives but never forgetting. Now it feels like my heart doesn't even exist. Our plans are nowhere near complete and without you there is no point."
Ms Bailey's brother, John, said it had been an "extremely difficult time" for her family.
Making a direct appeal to his sister, he said: "I know you had said you wanted some time and space and we don't want to intrude on that unless you want us to... All we need is some information that you are OK."
Chief inspector Julie Wheatley said it was a "highly unusual case" because Ms Bailey "seems to have simply disappeared".
"We literally have no trace of her despite extensive searches and inquiries which have been on-going since she was reported missing," she said.
"Whilst this very much remains a missing person's inquiry... as the days and weeks pass we and Helen's family and friends are becoming increasingly concerned for her welfare."
The force has asked for Ms Bailey, or anyone who knows where she might be, to contact them.

The blast, which destroyed an 80m (262ft) section of road, took place on the G30 expressway in Henan province.
China National Radio had put the number of dead at 26 but the report appeared to have been removed from websites.
Several vehicles were reported to have fallen to the ground 30m below.
Witnesses said some cars were thrown over the edge by the force of the blast, the cause of which was not immediately clear.
Six vehicles were retrieved from the wreckage, Xinhua said, while search and rescue efforts were continuing at the site. Eight people had been injured, the agency said.
Footage from state broadcaster CCTV showed rescuers digging through rubble. The channel said 10 trucks had been found under the bridge.
Images posted on microblogging sites showed wrecked trucks and debris, as well as a collapsed section of highway.
One photo showed a truck perched precariously at the broken edge of the carriageway.
The G30 is the longest road in China, running for 4,400km (2,700 miles) from the coast of eastern Jiangsu province to Urumqi, close to the Kazakhstan border.
Fireworks are traditionally set off in China to celebrate the Lunar New Year, which is just over a week away. There are frequently reports of accidents as they are being made, stored or transported.
The BBC's Jon Sudworth in Beijing says there has been much debate over whether the use of fireworks should be reduced, in part to help curb pollution.
Official statistics show that in 2011, more than 60,000 people were killed on roads in China. The deaths are often blamed on inadequate training, poor quality vehicles or on drivers ignoring safety instructions.
Earlier this month, China halted plans to introduce tougher penalties for traffic offences, following a public outcry.
The rules imposed penalty points for motorists who drove through amber traffic lights, with a driving ban after two offences, as well as increasing penalties for speeding, drinking and driving and using a mobile phone while behind the wheel.
But there were widespread complaints that drivers stopping abruptly at lights were ultimately causing more accidents.
The government said it was reconsidering its traffic policies.
One month after a missing children's author was last seen, her partner has said her disappearance has "shattered" the family.
[NEXT_CONCEPT]
A truck carrying fireworks has exploded on an elevated highway in central China, killing at least five people and causing part of the road to collapse, state media report.