Renewing his plea for information, Peter Lawrence said someone somewhere must know something about his daughter Claudia and now was the time to speak out.
Police believe the 35-year-old from York - who has not been seen since March 18 2009 - was murdered but her body has never been found.
Officers previously said they "strongly suspect key and vital information" which would offer a breakthrough in the case is being "withheld".
Nine people have been questioned as part of the investigation but no charges have ever been brought.
Mr Lawrence said: "It's difficult to know what happened.
"I've always said no matter your loyalties to someone else, you must see what effect this has had on the family.
"It's really time after 10 years to say what you know about what happened to Claudia.
"I know as well as the police that there must be someone who does know what happened.
"Please say something.
"People are still listening and people are still contacting the police in some way."
He spoke after welcoming the introduction of Claudia's Law, which came into force on Wednesday.
Not knowing what has happened to his daughter has taken an "enormous toll" on him but the campaign for changes in the law has been a help, he said.
Formally known as the Guardianship (Missing Persons) Act 2017, it allows relatives to take control of their missing loved ones' financial matters.
Under the law, families can apply to the High Court for guardianship of the affairs of a missing person after they have disappeared for 90 days or longer.
It will mean they can make mortgage payments and handle bills on their behalf.
Previously, a missing person had to be declared dead in order for someone else to manage their assets for them.
Mr Lawrence, who has campaigned tirelessly for the change since his daughter's disappearance and was made an OBE for his efforts, said the move will relieve a huge "burden" placed on families and the news would come as a "relief" for many.
He said hundreds of families would be "queuing up" to make use of the law.
At a press conference on College Green, Westminster, to mark the "historic" occasion, Mr Lawrence said: "For once there is good news today.
"It's been a long haul. We've been at this trying to persuade Government, Parliament and everybody since 2011. The Act was passed in 2017 and here we are in July 2019. But at least we are there.
"It means people can at last look after the property and financial affairs of their missing loved ones. I couldn't believe 10 years ago there wasn't any way of doing that. But there certainly wasn't.
"It's a great day. At last, the hundreds of families now have the opportunity to do things which all the rest of us take for granted day-to-day.
"(The law) allows them to stand in the shoes of those who are missing. But it has to be in the best interests of the person who is missing. After all, they may and hopefully will come back."
Thirsk and Malton MP Kevin Hollinrake, who has supported the Lawrence family in their campaign to change the law said: “I know from talking to Peter how incredibly difficult it can be if families have the additional worry about the financial affairs of their missing loved one, without being able to do anything about it.
I sincerely hope that his new law, which will enable them to take control of the finances to ensure that payments are kept up to date, will make a difference at a hugely emotional and worrying time.”