SRDS is an excellent resource for magazines and other types of media such as TV, radio, and websites. Includes links to media kits and target audience descriptions.
FOLIO, "the magazine for magazine management" is an excellent source for keeping up with news & trends in the magazine industry. Alden Library has both the print version (1972-2015) and the full-text online version (1998-2016).
To search for info on your magazine, click "Search within this Publication" in the online version and add the name of your magazine to the second search box.
Choose any of the online sources for this magazine and then click "Search within this Publication." Put the name of your magazine, the publisher or the name of key personnel in the second search box.
Use the Serials Directory to search for information on the magazine's niche or competition. Try searching for your magazine title and then use the subject category to find similar magazines.