Discovering Famous Monsters of Filmland with its first issues, he received regular acknowledgments and thanks as a contributor throughout the early years of the magazine, along with Don Glut, Eric Hoffman, and Mark Thomas McGee.
In the late 1960s and early 1970s, Warren made significant contributions to Walt Lee's three volume Reference Guide to Fantastic Films (Chelsea-Lee Books, 1973).
Warren was also a regular contributor to Leonard Maltin's Movie Guide, a book series of capsule film reviews that began in 1969; it was updated annually beginning in 1978.
In order to incorporate quotes from scores of filmmaker interviews conducted by Tom Weaver, and a number of color stills and film posters, a revised and expanded, 1040 page "21st Century" edition was prepared and released by McFarland in a large hardcover format in 2009.
In 1989, he created the ShowBiz Roundtable for the online service GEnie to generate discussions about films and other aspects of show business.
During the 1990s, he teamed with film director William Rotsler to produce segments surveying American television for the French TV series Destination séries.