纷纷【fēnfēn】

纷纷 goes before a verb and says many people or things did the same thing, one after another in quick succession. It's neutral to written and common in news reports.

The subject is a crowd

纷纷 describes many separate people or things acting. With one person it makes no sense, even if that person does the thing many times – for that, use 不断 or 一再.

• × 他纷纷表示同意 → 大家纷纷表示同意
• × 他纷纷问了很多问题 → 同学们纷纷提问

After a noun

纷纷 also stands after a noun as the predicate, meaning "many and scattered". The common phrases are 议论纷纷, "everyone is talking about it", and 大雪纷纷, "snow falling thick and fast".