Books about hitchhiking are plenty.
Hitch-Hiker's Guide to Europe by Ken Welsh: outdated but contains great information for Europe, North Africa, the Middle East and the "Communist countries." Was the inspiration for the title of Douglas Adams' Hitchiker's Guide to the Galaxy.
No Such Thing as a Free Ride? A Collection of Hitchers' Tales. Compiled by Simon and Tom Sykes (Great Britain: Cassell Illustrated, 2005). A 192 pg. compilation of hitch-hiking lore and experience, contributed by more than a hundred, from both sides of the experience, mainly British. A great sampling.
Derelict Days... Sixty years on the Roadside Path to Enlightenment by Irv Thomas. (Bloomington, IN: AuthorHouse, 2004). Personal tales from across a 60-year span of American (and some European) hitch-hiking, in a 226-page text. Mostly written at the time of each adventure, these highlight the consciousness-raising aspect of the experience. Included is a newspaper account of the earliest American hitch-hiker on record (1916).
The Hitchhiking Grandmother by Grace Small, as told to Ruth Barton Davis (Forest Grove, OR: Pilgrim Way Press, 1990). Quite remarkable life story of a 46-year old woman who took up hitch-hiking in 1941, indulging her adventurous spirit thusly for some 25 years, both in the US and Europe. The 200-page book is cheaply obtainable on bookfinder.com.
In Russian there are a lot of books about hitchhiking, Praktika Volnyh Puteshestvyi by Anton Krotov being the most famous and according to many essential reading material for hitchhiking in Russia - if you read Russian that is.