Find references in Assets:

[MenuItem("Assets/Find Refereces")]
public static void FindReferences()
{
    EditorSettings.serializationMode = SerializationMode.ForceText;
    string path = AssetDatabase.GetAssetPath(Selection.activeObject);
    if (!string.IsNullOrEmpty(path))
    {
        string guid = AssetDatabase.AssetPathToGUID(path);
        List<string> withoutExtensions = new List<string>() {".prefab", ".unity", ".mat", ".asset"};
        string[] files = Directory.GetFiles(Application.dataPath, "*.*", SearchOption.AllDirectories)
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            .Where(s => withoutExtensions.Contains(Path.GetExtension(s).ToLower())).ToArray();
        int startIndex = 0;

        EditorApplication.update = delegate()
        {
            string file = files[startIndex];

            bool isCancel =
                EditorUtility.DisplayCancelableProgressBar("Matching..." + startIndex + "/" + files.Length, file,
                    (float) startIndex / (float) files.Length);

            if (Regex.IsMatch(File.ReadAllText(file), guid))
            {
                var assetpath = "Assets" + file.Replace(Application.dataPath, "");
                Debug.Log(assetpath);
                Debug.Log(file,
                    AssetDatabase.LoadAssetAtPath<UnityEngine.Object>(assetpath));
            }

            startIndex++;
            if (isCancel || startIndex >= files.Length)
            {
                EditorUtility.ClearProgressBar();
                EditorApplication.update = null;
                startIndex = 0;
                Debug.Log("Matching Finished");
            }
        };
    }
}