The raids sparked fresh concern about deteriorating press freedoms on Turkey, which is gearing up for a November legislative election, its second in five months.
The crackdown saw masked police breaking into and searching a number of offices belonging to Koza-Ipek Media, which owns several newspapers and two television channels, the Dogan news agency reported.
Police entered 23 offices as well as Ipek University in Ankara belonging to its parent company Koza Ipek Holding "as part of a terrorist investigation into Fethullah Gulen", the state-run Anatolia news agency reported.
It said the conglomerate's chief executive, Akin Ipek, was overseas.
Ipek Media Group owns the Turkish dailies Bugun and Millet, the television channels stations Bugun TV and Kanalturk and the website BGNNews.com.
It was the latest move targeting supporters of the powerful "Hizmet" (Service) movement headed by Gulen, a former ally-turned-foe whom Erdogan accuses of trying to create a "parallel state" with the aim of overthrowing his government.
As Erdogan and his ruling Justice and Development Party (AKP) prepare for snap elections on November 1 under the shadow of a major offensive against Kurdish militants, opposition journalists have complained of a major squeeze on all critical media.
The swoop came a day after a court in Turkey's Kurdish-dominated southeast ordered two British journalists to be held on "terror charges".
The two work for the US-based media outlet Vice News in a case that has sparked fresh concern about press freedom.
Erhan Basyurt, editor-in-chief of the Bugun daily denounced the raids on Twitter.
"A police operation that aims to silence our group has started. Police raided our office. How shameful!" he wrote.