Google+ uses the “Open Graph” tags to get the thumbnail image, title and description of your post:
You need to setup a special meta tags, defining what image, title and description should be used,
for example: <meta property=”og:image” content=”https://url.of.your.image.jpg” />SNAP for WordPress plugin has built-in support for OG: meta tags: Plugin Settings->Other settings->”Open Graph” Tags-> Add Open Graph Tags It’s very basic, but it should work. There are several plugins specifically for OG: tags and almost all top WordPress SEO plugins have ability to add them.