Police spokesman Roland Ekkers said the girl, who has not been identified for privacy reasons, turned herself in to Rotterdam police in the company of a parent Monday and is now being interrogated.
The girl's tweet read, "hello my name's Ibrahim and I'm from Afghanistan. I'm part of Al Qaida and on June 1st I'm gonna do something really big bye."
The account's handle came with the nickname "Sarah" and a profile image of a young woman.
American Airlines responded a tweet that read, "Sarah, we take these threats very seriously. Your IP address and details will be forwarded to security and the FBI."
After that, the girl sent several apology tweets saying it was all a hoax.
Other people have followed with their own tweets, threatening American Airlines and other carriers.
(The Associated Press contributed to this report)