the network is just too big to just shut down because of holidays! not to mention it is global and not the whole world is celebrating Christmas. on top of that many nodes are hosted on servers (like Amazon) which will never shut down. and if that is not enough there are a lot of businesses that run 24/7/365 that run nodes as long as they are up and running.
if you can't find connection the first assumption should always be that something is wrong on your end, which in this case it is.
simply go on one of these sites that were mentioned in this topic, take an IP address of a well connected node and use the "addnode" RPC command to add it manually and see what happens:
https://bitcoincore.org/en/doc/0.16.0/rpc/network/addnode/or use one of the fallback nodes:
https://en.bitcoin.it/wiki/Fallback_Nodes#IPv4_Nodes