The Christian actor said the imposter has sent perverted messages to many of his female fans on Facebook.
He encouraged his followers to be aware of the "potential predator" and to spread the warning to young people who are particularly vulnerable to fraud.
He demanded the fraudster to stop, and ended the post with "Go find Jesus. Praying for you."
Pratt's real Facebook page has 3.7 million followers.
He usually uses his social media pages to share humorous behind-the-scenes photos and videos on projects he's working on, as well as posts of his son Jack.
Pratt, who announced in August that he and his wife split after eight years of marriage, shared with magazines earlier this year about how he became a Christian.
