using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		string input = "Welcome {{friend}} Get my new {{id}} with {{anonymous}} People";
        Dictionary<string, string> mydict = new Dictionary<string, string> ();
        mydict.Add("friend", "<<My Friend>>");
        mydict.Add("id", "<<Your ID>>");
        string pattern = @"{{(.*?)}}";
        string regex = Regex.Replace(input, pattern, delegate(Match match) {
           string v = match.Groups[1].Value;
           return mydict.ContainsKey(v) ? mydict[v] : v;
        });

        Console.WriteLine(regex);
	}
}