thank you for

1.（1）for 是介词+名词
Thank you for your help.
（2）for 是介词+动词ing
Thank you for helping me.
2. how are you doing

thank you for doing sth.

so, helping

1.Thank you for your help.
2.How are you doing?

Thank you for your help.
How is everything with you?

help
how do you do

Thank you for your help(名词）/helping me（动词） How are you？（非初次见面）=How do you do?(初次见面），严格说无同义句。