FindMissingReferences

using UnityEngine;
using UnityEditor;
using System.Collections;

public class ToolTest : MonoBehaviour {

	[MenuItem("Tools/Find Missing references in scene")]
	public static void FindMissingReferences()
	{
		var objects = GameObject.FindObjectsOfType();

		foreach (var go in objects)
		{
			var components = go.GetComponents();

			foreach (var c in components)
			{
				SerializedObject so = new SerializedObject(c);
				var sp = so.GetIterator();

				while (sp.NextVisible(true))
				{
					if (sp.propertyType == SerializedPropertyType.ObjectReference)
					{
						if (sp.objectReferenceValue == null && sp.objectReferenceInstanceIDValue != 0)
						{
							ShowError(FullObjectPath(go), sp.name);
						}
					}
				}
			}
		}
	}

	private static void ShowError (string objectName, string propertyName)
	{
		Debug.LogError("Missing reference found in: " + objectName + ", Property : " + propertyName);
	}

	private static string FullObjectPath(GameObject go)
	{
		return go.transform.parent == null ? go.name : FullObjectPath(go.transform.parent.gameObject) + "/" + go.name;
	}
}