Many of NokScoot pilots are SE asians pilots flying on a Thai validated license. I seen ads that they are currently recruiting foreign FO's and Capts. However, new aircraft delivery has been pushed back to March so there may be a delay there.....
Nok has about 10 foreign Capts on the NG (US, Serb, Dane, Brazilian, Spanish and even a Russian) and a few on the Q400 with more coming. (3 of the 10 on the NG were City Airways Capts who needed a gig after CA lost their AOC). But no more NG recruitment until 2017 it seems.
Thai Lion has around 30 non SE Asian Capts (mainly europeans & US) and around 40 Malay or Indo Capts. The total around half their Capt numbers.
New Gen and Siam Air obviously have foreign pilots too. Apparently Bangkok Airways is looking to recruit foreign Capts soon.
There are just not enough experienced Thai Capts to handle operators expansion plans.