Instagram Tips:

Block Login Popup:
Sometimes you want to scroll to the bottom of giant instagrams without logging in.

Add to uBlock Origin filters:
> instagram.com##.RnEpo
> instagram.com##body:style(overflow: auto !important)

Search Tools:
https://mulpix.com
http://gramfind.com
https://gramuser.com
https://toptager.com/ (don't include "#" in the search)
https://www.combin.com ($10/month)
https://phantombuster.com ($30/month)

Web Viewers:
https://tofo.me
https://pinsta.me/

NOTE: Even if a search tool says the user doesn't exist or have any posts, they may still exist and have posts.

For Programmers:
A few months after Q showed up, Instagram set a timeline for removing nearly all useful API features by July 2018. Maybe you can still pull likes and comments. The API will be completely killed in early 2020. Keep this in mind when looking into paid tools.

https://developers.facebook.com/blog/post/2018/01/30/instagram-graph-api-updates/

Research:
https://www.socialinsider.io/social-media-studies/Instagram-Hashtag-Study.pdf
https://sproutsocial.com/insights/instagram-stats/