I am waiting on my company to send me a new W2, as mine went missing. I worry that it will not arrive in time. What should I do? I don't know any data from the W2 either.

[redford-blade]

I went to set up an extension but I don't know how much taxes I owed for 2018 or how much I have already paid.

[KittyM]

You can submit an extension with a "guesstimate" from your final pay stub for the year or any other information you have.  

You can also submit an extension will all zeros, but if it turns out that you owe, you may have to pay a penalty for late payment of tax.