Protesters gathered outside the British consulate in Hong Kong Wednesday evening to voice shock and dismay at the detention of a consulate staff member by mainland Chinese authorities. Geng Shuang, a Chinese foreign ministry spokesman, said earlier Wednesday that Simon Cheng, a 28-year-old Hong Kong citizen, was being held in the neighboring Chinese city of Shenzhen for a legal violation. Hong Kong’s government-funded broadcaster, RTHK, quoted Geng as saying “The person you mentioned has been placed in administrative detention for 15 days as a punishment” for breaking a public security law. Cheng, a trade and investment officer at the consulate, was reported missing after he failed to return from a business trip to the neighboring Chinese city of Shenzhen on Aug.