Aggregate new home sales at China’s 100 largest developers have fallen every month on a year-on-year basis since last July. Global investors and home buyers in China are losing confidence in the country’s property market, which has entered a new stage of turmoil after a year-long slide in sales, stalled projects and mounting real-estate developer defaults. This week, a movement among frustrated homeowners who have threatened to stop paying their mortgages on unfinished homes quickly gathered steam on Chinese social media. People all over the country declared that they would do the same if developers don’t fulfill promises to deliver apartments that were earlier presold.