Can't login!

can't login either. PTC account.

this website can be helpful,
http://downdetector.com/status/pokemon-go/map/

That has happened to me... never for a full day... but after a couple hours i was able to log back in. Try waiting it out.

I haven't been able to log in

Same here, since some time last night. PTC account as well. Going on close to 10 hour outage now.

Edit - Finally working again for me after about 12 hours.