The Term Trekkie can be seen in the novel "the great trek" by E.A. Walker, of course at this point it had no relation whatsoever to Star Trek.
More than 30 years ago, A Science Fiction editor by the name of Art Saha applied the word Trekkies to Star Trek fans when he saw a group of Star Trek fans wearing pointed ears at a Science Fiction convention.
"Nah... John's more of a Trekker. At least he doesn't go to half a dozen conventions a year dressed as a Klingon."