Trang is a city in southern Thailand.
Hitching out
South towards Satun
In direction south you will have to use the airport road, but apparently there is no public transport there and it's quite a walk. You can take a Tuk-Tuk to the Tesco supermarket on that road and then walk a little further south where the bypass merges into the airport road. This makes a good spot to hitch.
South towards Hat Yai, Malaysia
You can walk or take a bus to the bus station East of the town. Then walk about 200 m along the main road and just hitch there. It should be easy to get a ride to Patthalung where you can let your driver drop you off right at the Suratthani-Hat Yai-highway.