The sample letter given below will demonstrate how a letter of appreciation should be written

AZ, Inc
Street
City,State,Zip Code
Date MM/DD/YYY

Dear Mr. Peters
Your Involvement and your wonder ability to motivate your employees has led to a significant amount of increase in the productivity and in turn the profitability.
AZ, Inc appreciates your amazing effort and your ability to provide guidance to your co-workers. If there is an award to be given to the best performer, its very much sure that you will be the one to get it.

Please accept my sincerest gratitude for your excellent performance.

Signature

John Matthew
Manager