51, as a popular community in China, has launched a "Question Plaza" with quite a number of participants. The discussion on certain topics is really热烈~~~~~~ (Note: "热烈" should be replaced with "lively" or "intense" in English for better expression.)
Revised sentence: 51, as a rather popular community in China, has launched a "Question Plaza" with a large number of participants. The discussion on certain topics is really intense.