1888, South African, "party of trekkers" (see trek). Meaning "fan of the television program 'Star Trek' " attested by 1976.
Online Etymology Dictionary, © 2010 Douglas Harper
Examples from the Web for trekkie
A trekkie will, however, drop everything to discuss the merits of Klingon spirituality.‘Star Trek’ for Dummies: Get Ready for ‘Into Darkness’ With Our Primer
May 14, 2013
Zwillich knew the image would lay bare his Trekkie obsession to friends and followers.Foursquare's Stalker Problem
Lisa Riordan Seville
August 8, 2010