McClure's Magazine
Since muckraking and investigative journalism was a somewhat risky type of media to publish, many major news outlets were not reporting on the controversial topics that muckrakers reported on. Then came the illustrated monthly periodical, McClure's Magazine. Started by S.S. McClure and John Sanborn Phillips in 1893 the periodical published novels in progress, usually a chapter a time. Many famous writers such as Arthur Conan Doyle and Mark Twain found this method of releasing work to be very progressive and chose to release works entirely within the magazine. Those big names gave the magazine some popularity which is what the magazine needed, as the goal of many of it's lesser known writers was to bring corruption and social injustices to the attention of the public.
Dozens of muckraking works were published in the magazine, including Ida M. Tarbell's The History of the Standard Oil Company, which was a big factor in the busting of the oil monopoly in the United States. Another important piece in the magazine was The Shame of the Cities by Lincoln Steffens, which exposed the corruption of local governments in several U.S. cities.
Unfortunately there was a dispute between the more prominent muckrakers associated with the magazine and S.S. McClure that resulted in their resignation. They went on to start The American Journal, which continued their careers as leaders of reform and left McClure without the content his readers wanted. The magazine was restructured and renamed a few times until it's final issue was published in 1929.