Philanthropist Tom Steyer stands in front of one of the billboards he has funded in Times Square calling for the impeachment of President Donald Trump on November 20, 2017 in New York City.

Billionaire activist Tom Steyer will push $30 million into an effort to boost millennial voter turnout in this year's midterm elections to help Democrats take over the House.

The former hedge fund manager, who made the announcement Monday, will not run for office in California this year. Rumors had swirled around whether he would challenge Sen. Dianne Feinstein for her seat later this year.

"I'm not going to run for office in 2018. That's not where I can make the biggest difference," Steyer said at a news conference in Washington.

Steyer raised his profile by launching national advertising campaigns in October calling for President Donald Trump's impeachment. He reportedly spent about $20 million on his Need to Impeach campaign and pressured Democrats to remove Trump from office if they win the House majority in the 2018 elections.

His voter turnout campaign, called NextGen Rising, said it will target more than 30 seats. It said it aims to "register more than 250,000 young voters."

"I'm putting $30 million behind NextGen America's youth organizing program to unleash the full political power of young voters ... They are horrified by what's happening in Washington D.C.," Steyer said on Monday.

The campaign will be active in 10 states: Arizona, California, Florida, Iowa, Michigan, Nevada, New Hampshire, Pennsylvania, Virginia and Wisconsin, Steyer said.

His campaign will go after notable Republicans such as House Speaker Paul Ryan, R-Wis., and Rep. Darrell Issa, R-Calif., in the Nov. 6 midterms.

The Washington Post first reported on Steyer's plans.

In a statement, Republican National Committee spokesman Michael Ahrens said "Tom Steyer can light as much of his money on fire as he wants," but it "doesn't change that Democrats like Nancy Pelosi view him as a distraction."

"If Democrats' message for 2018 is a baseless impeachment threat that the majority of voters disagree with, they're going to lose," he said.

Steyer, who retired from his hedge fund Farallon Capital in 2012, has pushed millions of dollars to Democratic candidates and causes in recent years. He started NextGen America, a political organization that supports liberal positions on climate change, immigration and health care, among other issues.