Many people have a thing for tickling. It is not that uncommon, but most people are not so into it that they join this forum for instance. Tickling is one of the most commonly used flirting methods, and girls many girls love tickling. Go on google and type in "do girls like being tickled" and you'd be surprised at how many girls write in how they love when their bf's tickle them.
I mean, look at it this way, you must've been into tickling before this forum. Chances are this forum just further enhanced your love for tickling. I myself have had a thing for tickling since I was very young, but never even thought anything of it until I discovered this forum one day and realized that liking tickling can be taken to a whole higher level. Many otheres out there, including celebrities, probably have very similar feelings about tickling that we all had before discovering this forum, but obviously because they cannot risk having a fetish brought to the publics attention it is very unlikely that they would want the term "tickle fetish" stuckin in the search engine of their computer.