The 55-year-old actor, singer and TV presenter has vanished from the social media platform, where he often engaged with his 503k followers. It is not clear if he deleted his account or has been banned.
Shortly before Barrowman's account became inactive he had responded to a fan who shared a video clip of him and Keeping Faith star Myles at a press conference saying they would do anything for each other.
The fan asked: "Not saying anything else, and I kinda don't want to bring this up, but whatever happened to this? Especially that last part."
Barrowman replied: "One is telling the truth! One is spewing rhetoric for an audience..."
The Doctor Who star posted a video on Instagram five days previously saying: "I just wanted you all to know that I have had some pretty bad news and I am devastated. And when I am able to talk about it I will. And to let you know that I am thinking about you and I appreciate you."
He then appeared to become emotional as he ended the video saying: "That's all I want to say."
The former Dancing On Ice judge made a public apology last years after he was accused of sexual misconduct on the set of Torchwood.
The actor claimed he exposed himself as a prank claimed he did it to put people at ease, but apologised for any offence caused.
The Scottish-born American actor - who lives with his partner of 29 years Gill - is best known for playing Captain Jack Harkness in Doctor Who spin-off Torchwood.
Welsh actor Myles, 44, played police officer Gwen Cooper in sci fi series Torchwood, which was filmed in Cardiff. She also stars in hit BBC Wales thriller Keeping Faith.
Watch: John Barrowman shares footage of Berlin traffic incident on social media