What started as criticism over errors in recent YouTube videos has escalated into allegations of sexual harassment, prompting the company to hire an outside investigator.

Linus Media Group CEO Terren Tong also responded via email, saying he was “shocked at the allegations and the company described” in Reeve’s posts. He went on to note that “as part of this process, beyond an internal review we will also be hiring an outside investigator to look into the allegations and will commit to...