Earlier quoted context omitted.
>they have done a relatively good job with Instagram and WhatsAp WhatsApp announced that they'll introduce ads, and the co-founder left the company due to privacy concerns.
That has nothing to do with whether WHatsapp will continue to grow or not.
Depending on the intrusiveness of the ads, users may opt to move to another platform, which will lead to more people being pulled away from Whatsapp. FB will have to monetize aggressively to recoup investments and keep wallstreet happy, but users may not be very receptive to ads within their messaging platform.