[googlethrow]

Googler here: The google performance and promotion process does, in fact, rely on reviews from your peers. The process happens once every 6 months, every other being non-mandatory.

Although your peers saying you were helpful is not enough, you need to demonstrate impact (and other attributes depending on your level).

[taurath]

"Demonstrating impact" of course meaning that you need to find peers willing to quantify your help in order to help you through the promotion process.