Joyce, who lives in north London, was last seen on July 31 and reported missing on August 7.
On Friday afternoon, the police appealed for help in finding Joyce.
Several hours later, her boyfriend, Brandon Mehmed, also a YouTuber, tweeted: "Everything is being dealt with in a professional manner. Please don't worry about her as she is safe and well (you have my word for that)."
When contacted by CNN for clarification Mehmed said she had been found by police, which London's Metropolitan Police then confirmed.
Joyce, who has over 2 million subscribers on YouTube, began trending on Twitter in July 2016, after her videos and social media posts alarmed fans. After sharing a video promoting a dress collection, in which she appeared nervous and distracted, some began to speculate that she had been kidnapped and forced to film the video.
The hashtag #SaveMarinaJoyce was shared over 3 million times before Joyce tweeted that she was "TOTALLY fine." In a YouTube video the following year, she told her viewers: "I simply don't want you to believe any of the conspiracy theories because none of them are true."
Joyce explained that she had depression, and was experiencing "one of the most horrible times of (her) life" when her behavior worried fans.
The most recent video on her YouTube channel, titled, "HOW I CARE FOR MY HAIR," was uploaded on June 21.