The two main support levels are 280 and 245 respectively. A break below 245 will be incredibly bearish for the stock. This scenario would assume a broad market sell-off, particularly in tech.
Chart:
FB on a 25% decline + expected movements + Strategy. by ThinkingAntsOk on TradingView.com
Credits: https://www.tradingview.com/chart/FB/ZbdCuiVl-FB-on-a-25-decline-expected-movements-Strategy/