The lawsuit accuses the company of "surreptitiously" taking content without user consent.
Owned by Beijing-based ByteDance, TikTok has built up a keen US fan base.
TikTok, which is thought to have about half a billion active users worldwide, has previously said it does not store US data on Chinese servers.
However, the platform is facing mounting pressure in North America over data collection and censorship concerns.
The lawsuit filed in a Californian court last week claims TikTok "clandestinely... vacuumed up and transferred to servers in China vast quantities of private and personally-identifiable user data".
It alleges the data could be used to identify, profile and track users in the US "now and in the future".
The plaintiff is named as Misty Hong, a Californian-based university student. Ms Hong claims she downloaded the app this year but did not create an account.
Months later she alleges the firm had created an account for her, and "surreptitiously" took draft videos she had created but never intended to publish.
The data was sent to two servers in China, backed by Tencent and Alibaba.
The lawsuit also argues TikTok unfairly profits from "secret harvesting" of private data by using that data to derive "vast targeted-advertising revenues and profits".
TikTok did not immediately respond to requests for comment.