March 3 (Reuters) - Britain's privacy watchdog, the Information Commissioner's Office, on Monday launched an investigation into how TikTok, Reddit RDDT.N and online image sharing website Imgur safeguard children's privacy.

Social media companies use complex algorithms to prioritise content and keep users engaged. However, the fact that they amplify similar content can lead to children being influenced by increasing amounts of harmful material.

The watchdog said it is probing how ByteDance's short-form video-sharing platform TikTok uses 13–17-year-olds' personal information to suggest content in their feed.

Social media platform Reddit and Imgur are being investigated over how they assess the age of their child users, it said.

"If we find there is sufficient evidence that any of these companies have broken the law, we will put this to them and obtain their representations before reaching a final conclusion," the Information Commissioner's Office said in a statement.

TikTok, Reddit and Imgur did not immediately respond to a Reuters request for comment.

Britain has previously passed legislation that set tougher rules for social media platforms, including a mandate for them to prevent children from accessing harmful and age-inappropriate content by enforcing age limits and age-checking measures.

Social media platforms including Facebook, Instagram and TikTok are required to "tame" their algorithms to filter out or downgrade harmful material to help protect children under proposed British measures published last year.

(Reporting by Angela Christy and Mrinmay Dey in Bengaluru; Editing by Lincoln Feast.)

((AngelaChristy.M@thomsonreuters.com;))