Employee advocacy is undeniably powerful. And so it should be. Humans are social by their very nature, and by virtue of this, they amass high-value networks that know and trust their opinions. Unsurprisingly, if you can successfully leverage the power of your colleagues' respective networks to the benefit of your company, you can make some pretty major waves.
I do think that such initiatives should come with one rather large caveat though, and that is:
The content that your colleagues disseminate must be relevant.
Relevant to the audience, relevant to the person sharing the content, and relevant to your brand. Getting even one of these three wrong can quite quickly undermine the objective in hand.
This may seem rather obvious, but you'd be amazed how many people get this wrong.