Which Turtle Beach headset? If the entire microphone came off and you lost it, then you are either going to need to find it or buy a replacement microphone. There is no possible way to talk to your friends online without a microphone.
First of all what model/style do you have? My son had the same exact problem, and we ended up having to replace the entire headset! If you have your receipt and/or warranty, then you should contact: http/www.turtlebeach.com/products/headsets/pc?gclid=CNHG8KPVhsoCFYU-aQod80MM9Q
and ask them what you should do.!
Good Luck!