Thanks for the question. After seeing your username, I had to see if Robert Plant was still alive, or like so many other rock n rollers, OD'ed. It appears that his sexual exploits and intense partying lifestyle got to him, as in 1975 his hedonistic lifestyle came to a reality when a terrible automobile accident that seriously injured him and his wife caused him to re-think his entire world view. (Take after your mentor MRP2009, "re-think your world view").
To answer your question: while polygamy is undoubtedly on the minds of the radical gay lesbian bisexual transgender movement once they've sliiiiithered into the institution of marriage (why wouldn't it be, anonymous sex with HUNDREDS of different partners is part of their "identity"), I would hardly call a group of teenagers going to a social event a "polygamous act".