The bash took place at Paul's mansion in a gated community in Calabasas, California. The mom claimed that her daughter and eight other girls ended up in the hospital after somebody slipped an unknown drug into their drinks.
"The girls were all half-naked and unable to walk or talk," the mom said in a Facebook post.
The Los Angeles Sheriff's Office said it is looking into "a possible single occurrence of unwillful impairment."
And a neighbor of Paul said she was hurt as a partygoer tried to get into her home and she fell.
Paul has 18 million followers on YouTube and is famous for his rowdy stunts.
In a statement to Inside Edition, Paul's lawyer, Larry Stein, said, "We take this claim very seriously, and are working with authorities to make absolutely sure we do our part to uncover the truth," Paul's lawyer said.
No one alleges Paul had anything to do with the reported incident.