I saw people spawning in facing different directions, so there's no telling. Without a compass, you have no chance of finding your way back. I headed slightly south, south-east... and ended up reaching the southern coast before I saw a tree. Headed east for another 10 minutes maybe, and finally found the treeline. I ran back more to see if it could be done... but I think I probably ran for 2.5 hours before finding the coast. If you do run back, head directly SouthEast and you might get lucky and hit the NW corner of the map.