I signifies that the broadcasting agency expects to have more information shortly, so you don't need to channel surf to find more.
Figuratively, a person might say it about himself, indicating that he will have more information shortly. It's kind of joking when a person says it.
1) The date for the trip to Macau may change, stayed tuned.
> This is a run-on sentence, a comma splice joining two separate sentences instead of a period (or semicolon or conjunction)
- The date for the trip to Macau may change. Stay tuned.
2) There are some more information about this topic, stayed tuned.
> Also a run-on sentence
> "Information" is construed as singular
- There is more information about this topic, so stay tuned.
3) Stayed tuned in the upcoming changes in the situation / decision.
> This is a fragment.
- Stay tuned for (more news about any) upcoming changes in the situation / decision.