The lawsuit seeking unspecified damages was filed in Manhattan federal court Tuesday by a man who remains anonymous.
The man says he met Kevin Clash on a chat line when he was 16 years old in 2000 and exploring modeling opportunities in New York.
The lawsuit says Clash had numerous Elmo dolls in his apartment when he met the teen for sex. The man, now 29, is the third to make claims against Clash, who resigned from "Sesame Street" last week after 28 years.
A spokeswoman says Clash "believes this lawsuit has no merit."