A lot of popular Vine users are no longer active on the platform

"Once a social media darling, Vine is falling out of favor. After analyzing 9,725 Vine users with more than 15,000 followers, influencer marketing company Markerly found that 52 percent of them have exited the platform since Jan. 1. Instead, they have moved to YouTube and Snapchat for different reasons.
“I used this account a lot before Snapchat came out,” influencer Nash Grier wrote in his Vine profile.
The finding may not surprise many. Compared to Vine, Snapchat offers features like geofilters, 3D stickers and My Story that allow would-be influencers to create more vivid in-the-moment content than they used to share on Vine. YouTube, on the other hand, lets creators make more polished long-form video content, which is becoming appealing to more and more Vine stars. For example, Zach King, one of the biggest celebrities on Vine, started to move his content over to YouTube where he updated three or four times a month. His most recent Vine clips, in comparison, were posted in January."
Source:  Digiday, 17th May 2016
Note - Zach King has started posting again