A very insightful article dating back to 17 December 2011, showing how Luther's message spread via the equivalent of social networking in his day:
"Although they were written in Latin, the “95 Theses” caused an immediate stir, first within academic circles in Wittenberg and then farther afield. In December 1517 printed editions of the theses, in the form of pamphlets and broadsheets, appeared simultaneously in Leipzig, Nuremberg and Basel, paid for by Luther's friends to whom he had sent copies. German translations, which could be read by a wider public than Latin-speaking academics and clergy, soon followed and quickly spread throughout the German-speaking lands. Luther's friend Friedrich Myconius later wrote that “hardly 14 days had passed when these propositions were known throughout Germany and within four weeks almost all of Christendom was familiar with them."
"The unintentional but rapid spread of the “95 Theses” alerted Luther to the way in which media passed from one person to another could quickly reach a wide audience. “They are printed and circulated far beyond my expectation,” he wrote in March 1518 to a publisher in Nuremberg who had published a German translation of the theses. But writing in scholarly Latin and then translating it into German was not the best way to address the wider public. Luther wrote that he “should have spoken far differently and more distinctly had I known what was going to happen.” For the publication later that month of his “Sermon on Indulgences and Grace”, he switched to German, avoiding regional vocabulary to ensure that his words were intelligible from the Rhineland to Saxony. The pamphlet, an instant hit, is regarded by many as the true starting point of the Reformation."
"Unlike larger books, which took weeks or months to produce, a pamphlet could be printed in a day or two. Copies of the initial edition, which cost about the same as a chicken, would first spread throughout the town where it was printed. Luther's sympathisers recommended it to their friends. Booksellers promoted it and itinerant colporteurs hawked it. Travelling merchants, traders and preachers would then carry copies to other towns, and if they sparked sufficient interest, local printers would quickly produce their own editions, in batches of 1,000 or so, in the hope of cashing in on the buzz. A popular pamphlet would thus spread quickly without its author's involvement.
As with “Likes” and retweets today, the number of reprints serves as an indicator of a given item's popularity. Luther's pamphlets were the most sought after; a contemporary remarked that they “were not so much sold as seized”. His first pamphlet written in German, the “Sermon on Indulgences and Grace”, was reprinted 14 times in 1518 alone, in print runs of at least 1,000 copies each time. Of the 6,000 different pamphlets that were published in German-speaking lands between 1520 and 1526, some 1,700 were editions of a few dozen works by Luther. In all, some 6m-7m pamphlets were printed in the first decade of the Reformation, more than a quarter of them Luther's."