If your goal is reaching people who have never seen you, the platforms' own collaboration features outperform every tagging tactic by a wide margin.
Why they work so well
A co-authored post appears natively in both audiences' feeds and both profile grids, with engagement pooled into one post. It is not a mention or a share — it is the same post, distributed twice. No tag configuration produces anything comparable.
The forms available
Instagram collab posts, appearing on both grids. TikTok duets and stitches, which build on someone else's content. YouTube collaborations and shorts remixes. LinkedIn co-authored articles and document posts. Each puts your work in a room you did not have access to.
How to get them
Not by cold-pitching accounts far larger than yours, which almost never works. By engaging genuinely with accounts at roughly your size for a while first, then proposing something specific that benefits both audiences.
Specificity matters enormously. "Want to collab?" gets ignored. "I'd like to make a piece comparing our two approaches to X, filmed separately, published as a collab post on both" gets a reply.
Where tags still fit
The collab brings the audience; the tags still classify the post for search and long-tail discovery afterwards. Do both — just be honest about which one is doing the heavy lifting.