fanatic

groupie

admirer, amateur, collector, connoisseur, dilettante

authority, expert

adherent, convert, cultist, disciple, follower, hanger-on, votary

advocate, apostle, backer, champion, evangelist, exponent, friend, patron, promoter, proponent, supporter

partisan (also partizan), zealot

booster, rooter, well-wisher

faddist

activist

dreamer, idealist, visionary

cultist, disciple, follower, hanger-on, idolizer, votary

addict, aficionado (also afficionado), buff, bug, devotee, enthusiast, fan, fancier, fiend, fool, freak, habitué (also habitue), head, hound, junkie (also junky), lover, maniac, maven (also mavin), nut, sucker

advocate, apostle, backer, champion, evangelist, patron, promoter, stalwart, supporter

booster, rooter, well-wisher

faddist