From the official site:
"THIS IS THE LAST SHOW TO BE ADDED TO OUR NORTH AMERICAN TOUR
SEE YOU ALL VERY SOON!
5/28 Portland, OR
Sunlight Supply Amphitheater
Pre-Sale: Thursday, March 24 10a-10pm PDT
On-Sale: Friday, 3/25 @10am PDT / 5pm GMT
Ticket link: http://www.ticketmaster.com/event/0F005075B1663F52"
Also, the 2 Live Nation presale codes are HITMAKER and COVERT. Ticket prices range from $17 - $92.
Note: For those of you who bought tickets to see The Twilight Sad in Portland on May 28th, that show has been rescheduled to May 30th. Tickets for the 28th will be accepted, but "Ticket buyers will be receive an email soon with info on how to get a refund if you can't attend due to date change".
Note 2: As a friend has pointed out, this "Portland, Oregon" show is actually in Ridgefield, Washington. As our Seattle friends will tell you, RS continues to be geographically challenged when it comes to the Pacific Northwest. :)