When sharing to Twitter, by default, the handle @ShareThis shows up. You can customize this to your own by implementing the following:
1. Select "Website" as a "Platform" and then select the "style" and proceed till end to get the code.
2. Once you get the code, you can directly add it to your Blog site code and at same moment you can edit the Twitter span tag and add "st_via" parameter to specify the Twitter Handle.
So that your Twitter span tag will look like:
<span class="st_twitter" st_via="YOUR TWITTER USERNAME"></span>
Also, you can use the parameter st_msg to change the message that gets tweeted.
Hope this helps and clarifies.
Please feel free to contact us if you face any issues during implementation.