Media company E.W. Scripps Co. SSP -3.23% has continued its push into podcasting with the acquisition of Stitcher for $4.5 million in cash.

Stitcher is a free app that streams more than 65,000 podcasts from publishers ranging from NPR to MSNBC to The Wall Street Journal. It will operate under Midroll Media, the podcast advertising company that Scripps acquired last year for $50 million, plus $10 million more over three years if the company hits certain milestones.

Midroll sells ads for about 230 programs like “WTF with Marc Maron,” “The Nerdist,” “StarTalk Radio” and “The Bill Simmons Podcast.” But podcast listeners these days have a handful of ways to actually tune into shows, through the likes of Apple’s podcast app or Google Play Music. Stitcher, one such service, has 8 million registered users and is installed in about 50 car models.

“We certainly have the ad sales force and the connections that make us a leader in the space, but today we depend almost exclusively on distribution into other channels,” said Adam Symson, chief digital officer at Scripps. “This puts in place, with a very strong brand, another piece of the puzzle in the ecosystem play.”

Scripps purchased Stitcher from Deezer, the French streaming company that acquired the service in 2014. A Deezer spokesperson declined to comment on the price, but a person familiar with the matter described it as a small “acquihire.” Before that deal, Stitcher had raised about $25 million in funding.

Stitcher’s dozen employees will join Midroll.

The acquisition comes as Midroll promotes its new Howl premium service, which offers original shows and ad-free archives of popular podcasts like “WTF with Marc Maron” for $4.99 a month. “At some point, the two will intersect,” Erik Diehn, vice president of business development at Midroll, said of Stitcher and the premium service.

As new listeners and shows enter the podcast world, companies in the space have been contending with a handful of industry challenges, like measuring audience size and wooing big brand marketers.

“For the first time we’ll have significantly more ability to help with podcast discovery, to help with distribution, to help shows grow, and to help find out what audiences want in a way that we could not do before,” Mr. Diehn said.

Scripps has been on the hunt for digital acquisitions as of late. In April, it purchased humor website Cracked from Demand Media for $39 million. In 2014, Scripps bought digital video news company Newsy for $35 million, but took a $24.6 million goodwill impairment charge on the business in the third quarter of 2015.

Last year, Scripps completed a merger with Journal Communications. The two companies combined and spun off their newspaper holdings, merging broadcast operations under Scripps.

Write to Steven Perlberg at steven.perlberg@wsj.com