Best way for this string.replace?

hoi all...
i have a string with some placeholders in it. this string is added to a StringBuilder in a loop. While adding it, i replace each placeholder with another stirng. currently it looks like this:
-----------
.... loop start...
listCode.Append(forumTemplate.getLoopCode().Replace(
    "[forumSubject]", forumSubject).Replace(
    stringPlaceholderOne, oneTopic.getReplyCount().ToString()).Replace(
    "[countViews]", oneTopic.getViewCount().ToString()).Replace(
    "[lastPostAuthor]", oneTopic.getLastPostAuthorNick()).Replace(
    "[lastPostDate]", oneTopic.getLastPostDateFormatted())
);
... loop end...
-----------

the code above has a problem:
If a placeholder variable ("stringPlaceholderOne") is an empty string (length=0), then the .Replace() throws an exception.

Question:
What is the best way to handle this?
I thought about a simple code like this:
-----------
static public string replaceInString(string inString, string inFind, string inReplaceWith) {
   if (inString.IndexOf(inFind) >= 0) {
      return inString.Replace(inFind, inReplaceWith);
   } else {
      return inString;
   }
}
-----------

But I believe there are better ways to do it... e.g. extend the normal string with my own replace method?
is this possible? how?
any other idea?

Thank you