The "Zozo" or "Zoso" demon myth was popular decades ago, but received new life with the advent of the internet. The name "Zoso" is most closely associated with the band Led Zeppelin. One of their albums had some artwork on it including a rune that looked like the English letters "ZoSo". Led Zeppelin has also been associated with satanism by fundamentalist preachers. For example, it was claimed that if you play Stairway to Heaven (a track on the "IV" album) backwards you hear satanic messages. Also, Led Zeppelin guitarist Jimmy Page bought Aleister Crowleys house. Jimmy also owned an occult book store and published one of Crowleys books. Crowley has also been associated with satanism although that's not quite right. He was an occultist with his own philosophy.
"Zozo" demonology (note the spelling difference) might have been practiced even earlier than that. In the Dictionnaire Infernal published in the early 1800's a demon named "Zozo" was described. Although he has a cute name that someone might give to a pet hamster, he's supposed to be pretty evil (I guess that's what demons do). So the coincidence of the Led Zeppelin "Zoso" rune looking quite like "Zozo" probably re-ignited the fascination and lore over this particular demon.
Anyhow, teenagers are the primary players of Ouija boards, and teenagers also listen to rock bands like Led Zeppelin (or at least they used to, back in the day). So with mysterious "zoso" name in their heads and the rumors swirling about Led Zeppelin, it really wasn't a stretch that Ouija players would push the pointer around to spell out that 4 letter name. And when they did, they were amazed and quickly spread the message to other friends. And with that power of suggestion, that's all it would take for those friends to also spell out "zoso" on their boards. And so on.
Regarding Ouija boards, it's a kid's game sold at Toys R Us, and it doesn't conjure spirits any more than Hungry Hungry Hippos conjures real hippopotamuses. It works based on the ideomotor effect -- subconsciously you are pushing on the pointer in the direction of the letter you think the "spirit" is spelling. And it works much better with multiple players, since when a few letters are already spelled everybody tends to home in on the same word -- the players are pushing the pointer, not a spirit.
http://www.zosoontour.com/
http://skeptophilia.blogspot.com/2014/08/the-creation-of-zozo.html
http://www.straightdope.com/columns/read/1955/what-do-the-four-symbols-on-led-zeppelins-4th-album-mean
http://www.jesus-is-savior.com/Evils%20in%20America/Rock-n-Roll/led_zeppelin.htm