ByteDance Ltd., TikTok’s parent company, has been replacing US-hired staff near Seattle with managers connected to China, aiming to replicate its e-commerce success in Asia after sales fell short in America.

TikTok Shop initially set a goal to increase its US e-commerce business tenfold last year to $17.5 billion in transaction volume, but had to drastically lower that objective, according to people familiar with the plan who spoke on the condition of anonymity because they were not authorized to talk publicly.

TikTok established its Shop business in the Seattle area near Amazon.com Inc., the online retail giant it ...