As you know Facebook announced their own cryptocurrency LIBRA but various legislation needs to complete before launched, so after launch can buy but this will be stable coin and will not affect BTC price.
There is no indication it will be a stablecoin. It will be on exchanges and will not be pegged to any fiat money like dollars, so it will move like all the othe other alts and be volatile. It will behave in the same way as the alts based on market conditions with same price movements.