"Surf's Up" as an expression means "The surf is up." Otherwise, if you mean "surfs up" as in "He surfs up and down the coast" or "She surfs up beside me," then in both cases the past tense is "surfed."
The past tense of surfs is surfed.
Guy's Grocery Games - 2013 Surfs Up 1-4 was released on: USA: 10 November 2013
emperor penguins are depicted in Surfs up emperor penguins are depicted in Surfs up
The Spine Surfs Alone was created in 2004.
Storage Hunters - 2011 Surfs Up in Canyon Country 3-8 was released on: USA: 28 July 2013
A surfer is someone who surfs the ocean.
The surfs fought in the Crusades because they wanted the same rights as the nobles.
Surfs Up Hang Ten Get Off My Wave Gnarly Wipe Out - 2011 was released on: USA: 18 September 2011 (New York Surf Film Festival)
She surfs
A seahorse!!
A surfer girl?