Well, this kind of scifi is bending the laws of physics. Thus, you can fully legit use hypothetical particles which aren't proofed to exist yet.

So your solution is as simple as it can be:

[Tachyon][1] 

> A tachyon /ˈtæki.ɒn/ or tachyonic particle is a hypothetical particle that always moves faster than light. [sic]

[...]

> They have been used as a standby mechanism upon which many science fiction authors rely to establish **faster-than-light communication**
[sic]

A common mechanic is sending a tachyon beam to the communication target. 
Behaves pretty much like any light beam (Just faster), can be detected or blocked by objects on their way.

  [1]: https://en.wikipedia.org/wiki/Tachyon