Return unique values

Hi I have a text box that has values separated by a comma. I am trying to remove the duplicate values for, example this text box will have values like:
John, Adam, Mike, John, Mike
I want it to return unique values like:
John, Adam, Mike

I found a VB function and converted it to C# but it's giving me errors like newArray is a variable but used as a method. Thanks
public string RemoveDuplicates(string items)
 {
  StringBuilder Result = new StringBuilder();
  Array newArray = default(Array);
  newArray = Strings.Split(items, ",");
  for (int i = 0; i <= newArray.Length - 1; i++)
  {
   if (Result.ToString.IndexOf(newArray(i).ToString()) == -1)
   {
    Result.Append(newArray(i).ToString() + ",");
   }
  }
  return ...