Dear Henry,
Thank you for finding my pet dog.I'm so grateful to you.
Last Saturday,I lost my pet dog when I walked in the park.I'm so sad at that moment.I tried my best to look for my dog , but failed.I even thought I can't see my dog again.And then,you found him and send him to me.I'm really very surprised and excited.I don't know how to show you my happiness!
The pet dog is important for me.He is like my friend and I can't live without him.You are so willing to help others.You're so kind.
Thank you again.And I hope you can come my home to have dinner tomorrow.
Yours
Frank
匆忙写的应该可以勉强应付一下.