Adaption of Aldo's JS code here: http://answers.unity3d.com/questions/372047/find-world-position-of-a-texture2d.html to C#

MeshPixelTools.cs

using UnityEngine;
using System.Collections;

public class MeshPixelTools : MonoBehaviour {

  // Use this for initialization
	void Start () {
	
	}
	
	// Update is called once per frame
	void Update () {
	
	}
	
	public Vector3 UvTo3D(Vector2 uv){
  
		Mesh mesh = GetComponent<MeshFilter>().mesh;
  		int[] tris = mesh.triangles;
  		Vector2[] uvs = mesh.uv;
  		Vector3[] verts = mesh.vertices;
  
		for (int i = 0; i < tris.Length; i += 3){
    		Vector2 u1 = uvs[tris[i]]; // get the triangle UVs
    		Vector2 u2 = uvs[tris[i+1]];
    		Vector2 u3 = uvs[tris[i+2]];
    
			// calculate triangle area - if zero, skip it
    		float a = Area(u1, u2, u3); if (a == 0) continue;
    
			// calculate barycentric coordinates of u1, u2 and u3
    		// if anyone is negative, point is outside the triangle: skip it
    		float a1 = Area(u2, u3, uv)/a; if (a1 < 0) continue;
    		float a2 = Area(u3, u1, uv)/a; if (a2 < 0) continue;
    		float a3 = Area(u1, u2, uv)/a; if (a3 < 0) continue;
    
			// point inside the triangle - find mesh position by interpolation...
    		Vector3 p3D = a1*verts[tris[i]]+a2*verts[tris[i+1]]+a3*verts[tris[i+2]];
    
			// and return it in world coordinates:
    		return transform.TransformPoint(p3D);
  		}
		
		// point outside any uv triangle: return Vector3.zero
 	 	return Vector3.zero;
	}
 
	// calculate signed triangle area using a kind of "2D cross product":
	public float Area(Vector2 p1, Vector2 p2, Vector2 p3) {
  
		Vector2 v1 = p1 - p3;
		Vector2 v2 = p2 - p3;
  
		return (v1.x * v2.y - v1.y * v2.x)/2f;
	}
}