Kelly Wallace is CNN's digital correspondent and editor-at-large covering family, career and life. Read her other columns and follow her reports at CNN Parents and on Twitter @kellywallacetv.

(CNN) When most people think about domestic violence, they probably think of physical, sexual or emotional abuse, but less well-known is how partners can use financial means to abuse and terrorize their partners.

Tennis superstar Serena Williams hopes to pull the issue out of the shadows. By speaking out and adding her name to the cause, she's trying to make more people aware of the perils of economic abuse and realize what they can do to help victims.

"While I was familiar with financial abuse, I really didn't realize that it happened in about 99% of domestic violence cases. That's a pretty insane number. That's basically every domestic violence case," Williams said. "I was really surprised at how prevalent it was and underexposed the issue of financial abuse was. Because of that, I kind of wanted to encourage others to stand up and speak up and speak out about financial abuse."

Economic abuse can take many forms: preventing a victim from attending a job or looking for a job, or harassing a victim while on the job; applying for credit cards in a victim's name without their consent and running up mountains of debt; and deciding when or how a victim can have access to cash or credit cards.

For a sense of how widespread the problem is, as Williams mentioned, nearly all domestic violence survivors -- between 94% and 99% of them -- also report some form of economic abuse, according to the National Coalition Against Domestic Violence

Victims of domestic violence lose eight million days of paid work each year, the coalition says. The cost of the abuse is more than $8 billion per year.

One in four women will probably be affected by domestic violence at some point in their lives, and finances are often one of the top reasons women can't leave an abusive relationship, experts say.

"There are so many ways that financial abuse can keep their victims trapped," said Williams, who is the new ambassador for the Allstate Foundation Purple Purse program. Purple Purse, founded in 2005, focuses on raising awareness and helping survivors find the tools they need to recover from financial abuse.

"If a woman's credit is ruined, she can't go out and move out and try and get a different apartment. She has to kind of stay where she is," Williams said.

Vicky Dinges, the senior vice president for corporate responsibility for Allstate, said victims face economic hardships even if they find a way to leave the relationship.

"One of those things that we see when a victim does leave safely, they have a hard time affording legal fees, trying to rent an apartment, trying to see their children if they have children," Dinges said.

In front of a hidden camera, passengers get into a Lyft car and come across a purple purse. Inside, they find a phone and see a series of abusive text messages.

The messages start focusing on finances: "You're too stupid to manage money?" "Just where do you think you're going to live?" "Good luck paying a lawyer when you have no money."

The passengers connect by phone with the victim and meet her in a coffee shop to return her bag. They ask whether she's OK, and then they leave. The film asks, "If you knew someone needed help, would you know what to do?"

As Williams said, "The film shows that you can't always see the signs of financial abuse, and certainly, people don't even know it exists."

Dinges said that often, friends and family members of domestic violence victims will say that they were aware that there was some sort of abuse going on but that they didn't know what kind of support to offer.

"The thinking behind the film is, we don't know what we should do, but it's on us to learn," she said. "One of the most important things for victims is to know that there is hope and there is help and to bring domestic violence into the natural mainstream conversation so that more people are aware of where they can direct people."

Resources include PurplePurse.com, which offers tips on how to have the conversation with a loved one. It also has financial tools, such as a curriculum to create a financial plan to leave an abusive relationship, with guidance on how to go about repairing credit and accessing small loans to rent an apartment for a family.

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Dinges said she believes that Williams, who follows in the steps of the initiative's former ambassador, Kerry Washington, can be instrumental in increasing awareness not only among women but among men.

"We feel that one of the solutions to ending abuse against women is a way to get men involved," she said. "Domestic violence isn't just a woman's issue. ... It's a societal issue, and it's going to take both men and women to see it, talk about it, find solutions to end it."

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While on leave from tennis and preparing for her first child with Reddit co-founder Alexis Ohanian, she said she's excited about getting involved in different causes. She recently joined the board of SurveyMonkey and has spoken about the need to bring more diversity to Silicon Valley.

She also continues to be active in other charitable causes through two funds, one in her own name and the other, the Williams Sisters fund, with her sister Venus.

"You know me; I really like to speak out and speak up and be a leader," she said. "This is just another step towards who I am."