Used book sellers can be a valuable source of information. Try one of the following:
A search by title and author may produce many editions, but you click a box to limit search results to items labeled as First Editions. [Note: this list may include misleading items such as first editions of anthologies or of different versions of the text! Look closely at the fine print.] Listings include images of the book cover, but beware the fine print: avoid images labeled "Stock Image" and be sure to look for "Bookseller Image" instead to be sure the cover is legitimate.
There are a number of bibliographic and reader's advisory sources that highlight editions, adaptations, and sequels. These are some of the best known starting points:
As a compilation of resources from libraries worldwide, WorldCat has records on just about any edition that exists of a text. Use the option to search by title, and look to the left side of the search results to see the various formats, which you can expand by clicking "See All."
For example, in a title search for the children's book Caps for Sale: A Tale of a Peddler, Some Monkeys and Their Monkey Business (1940) by Esphyr Slobodkina, the filters reveal not just multiple print editions and story book videorecordings, but music versions as well.
Editions: Search by title and after clicking on the book you are interested in, choose the "More About This Book" tab. If you scroll down you will see a list of ISBNs for various print editions of the book. You can then search these individually by ISBN in WorldCat to get information on the editions.
Sequels/series: You can also click on the author's name from the book record to see a list of their works in Novelist. That author page will often have a tab for "Series" that you can look at for different series the author may have written, including any that has your book.
To Be Continued (print only)
This book on reference in the Social Sciences, Health, and Education Library lists sequels for books by various authors. It does contain fiction back to the early 19th century, but it is not a comprehensive list of all sequels.