Unfortunately, there is no native twitter way to send an auto response / welcome message to the new twitter followers. i hope twitter will be implement it in the near future.

Tto create an auto response, you have to rely on a 3rd party service website called Tweet Later.

Please note that tweetlater.com currently redirects to its new homepage at http://www.socialoomph.com/

How to?

Step1.

Create an account at Tweet Later by clicking on the “Register” Link.
After registration complete and verified your account, click login.

Step2.

On the home page, click “Manage My Scheduled Tweets and Twitter Account Automation”

Step3.

Click ‘Add New Account‘. This will allow you to bind your twitter account with Twitter Later service.

Step4.

Select Twitter and click Continue.

Step5.

In this page, enter your Twitter user name and the password, fill the captcha, then  scroll down to the point shown below.

Select “Automatically send a welcome message to new followers. ” and type your desired welcome message at the text box. I just typed “Hi, Thank you for following me on Twitter”.

Finally, Scroll down to the very bottom of the page and Click “Save” button for the changes to take effect.