HONG KONG — CHINESE police are looking for one of China's most outspoken dissidents, Zhang Weiguo, who has not been seen by family or friends in Shanghai since last week.Mr. Zhang, former Beijing bureau chief for the semi-independent World Economic Herald newspaper, was last at his Shanghai home on June 27, said relatives speaking by telephone from Shanghai. That evening, after Zhang departed for a dinner with friends, police arrived to question him about his "overseas contacts," but left when Zhang failed to return. In recent days, police have questioned relatives about the journalist's whereabouts. Zhang's family members said they believe the journalist had left Shanghai, but did not know whether he was in hiding. Zhang has angered authorities by speaking out boldly since his release Feb. 12, after 20 months in jail for his activities during the 1989 democracy movement. On June 24, Zhang published a lengthy article in the Hong Kong newspaper Ming Pao describing in detail a dialogue with police. Police asked Zhang in late May to hand over notes and materials for a book on the late Herald editor Qin Benli, an advocate of press freedom. But Zhang refused. Despite harassment by police, Zhang has vowed to uphold his constitutionally guaranteed right to freedom of speech. In an interview last month with the Monitor, he said: "No matter what trouble I encounter, I will exercise my rights. I want to make these laws a reality instead of just a lie."