Mihai Moscovici, 25, who provided updates in English all day over Twitter, painted a more nuanced picture. He said the gathering on Monday night drew only several hundred people. The protesters agreed to gather the next morning and began spreading the word through Facebook and Twitter, inventing a searchable tag for the stream of comments: #pman, which stands for Piata Marii Adunari Nationale, Chisinau’s central square. When Internet service was shut down, Mr. Moscovici said, he issued updates with his cellphone.