No I am not.
To be fair, there's a lot of things I don't believe in. The following are (but not limited to) things I also don't believe to exist: Angels, Aliens (at least not intelligent forms that have visited Earth), Lizard People, the Illuminati, Ghosts, Vampires, Sasquatch, Chupacabra, a Flat Earth, a Hollow Earth, a Hollow Moon, Goblins, Merfolk, the ability to properly balance Azir as he currently exists, Weather Control, the Loch Ness Monster, the Lake Champlain Monster, the Jersey Devil, the Dover Demon, Dragons, Werewolves, Magic (Not to be confused with Magic: The Gathering), Psychic Powers, Super Powers, the Devil Bird of Sri Lanka, Mothman, Manbearpig, Jackalopes, Wendigo, Mongolian Death Worms, Time Travelers, Skunk Apes, Mediums, Zombies, Chem-trails, a Geocentrific Universe, Gremlins, Unicorns, Luck (both good and bad), Melon heads, the Megalithic Yard, Atlantis, and Leprechauns.
I think Yetis are on the more realistic end of the scale, but unless someone provides actual, verifiable scientific proof of a large, previously undiscoved hominid, I'm going to stick with "They don't exist".