I came across this word on a few different sites. Forvo, Wiktionary, and Google do not know this word! Here are a few phrases I came across:
пожалуйста пропиарьте хорошо?
Пропиарьте Мой Канал А я Ваш.
Ребят пропиарьте паже.
Пропиарьте канал пожалуйста скоро розыгрыш.
Пропиарьте сами себя!!!
Here's my best guess: The пиар part of the word sounds like PR (short for public relations) and so my guess that the word means something like "promote" as in "Please promote my channel." So пропиарьте could also mean share, but the underlying idea is to spread the word about a video or channel at a video sharing site in order to gain viewers or subscribers.
Am I close? In any case, is this a standard word in Russian or more of a recent invention?