Straight from the horse's mouth:
Los Angeles International Airport (LAX) Terminal Move
Thursday, March 23, 2017
On May 12 2017, Virgin America will move its location at Los Angeles International Airport (LAX) from Terminal 3 to Terminal 6. As of May 13 2017, Virgin America will be co-located with Alaska Airlines in T6, allowing for more seamless flight connections across the combined airline's network. Although the move will result in closing Virgin America's Loft, Virgin America First Class guests and Elevate Gold members will have complimentary access and Elevate Silver members will be granted access at a reduced rate to the Alaska Lounge in T6 through 2017. Beginning in 2018, all guests will be invited to become an Alaska Lounge member.
https://www.virginamerica.com/cms/traveler-alerts