Question : how to block web chatting such as IMVU ?

Is there a way to block web chatting such as IMVU ? Can I use my router to do it ?

Answer : how to block web chatting such as IMVU ?

nope. you cannot block those programs completely. Paul Piccard from ISS (www.iss.net) has authored a topic "Risk Exposure: Instant Messaging & peer to peer network" that deals with various IM clients and features and the way to mitigate those security issues that comes with that.  You need to engage your senior management & HR management for force discipline among your users regarding IM access.