WebAssist Social Media Share buttons are all PNG. You can use the WA Social Share Button plugin to generate your initial code and then if you want to replace any of the icons, you can edit the code manually.
There are SVG versions of social media icons available to download for free all over the web. I've attached one for you - save to the same folder as before and update the img tag on your page to for example:
<img src="webassist/social/icons/twitter.png" alt="Twitter" border="0" title="Twitter" />
