This is a StumbleUpon icon. We've made it in iOS style, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 13,300 icons, all in the same style and quality.
Idea of StumbleUpon Icon by Anonymous
We've received the idea on July 18, 2012 and created the icons on July 22, 2012
I know some have been already posted, but this unifies all of them plus more. 1. Soundcloud 2. Pinterest 3. Stumbleupon 4. Wikipedia 5. Instapaper 6. Tumblr 7. Dribbble