Vachel Lindsay on Hitch-hiking 

Nicholas Vachel Lindsay was an American poet who roamed the country exchanging poems for food and shelter. He lived from 1879 to 1931. In 1912 he took a long walk from from Illinois to Kansas and on Sunday morning, June 23rd wrote a letter home in which he said: 
    "When the weather is good, touring automobiles whiz past. They have pennants showing they are from Kansas City, Emporia, New York or Chicago. They have camping canvas and bedding on the back seats of the car, or strapped in the rear. They are on camping tours to Colorado Springs and the like pleasure places. Some few avow they are going to the coast. About five o'clock in the evening some man making a local trip is apt to come along alone. He it is that wants the other side of the machine weighed down. He it is that will offer me a ride and spin me along from five to twenty-five miles before supper. This delightful use that may be made of an automobile in rounding out a day's walk has had something to do with mending my prejudice against it, despite the grand airs of the tourists that whirl by at midday. I still maintain that the auto is a carnal institution, to be shunned by the truly spiritual, but there are times when I, for one, get tired of being spiritual."
This is the earliest clear reference to hitch-hiking that I've come across yet, though it doesn't use the word. It contrasts well with the earliest citation of the word we have dating back to 1923 (it appeared in The Nation) providing a gap of some 11 years during which it is easy to suppose that the phenomenon grew in the public awareness to the point where a new word was called for. This extract from one of Lindsay's letters was pulled from Adventures Rhymes & Designs (Eakins Press, New York, 1968, pp. 120-121) which is essentially an annotated reprint of Lindsay's book Adventures while Preaching The Gospel of Beauty (Mitchell Kennerley, New York, 1914).