using System;

using System.Text.RegularExpressions;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        String input = "one two three #abc four five six #xyz";

        var results = new List<string>();

        Regex regex = new Regex(@"([\s*\w]+ #\w+)");

        var matches = regex.Matches(input);

        if (matches.Any())

        {           

            foreach (var match in matches)

            {

                results.Add(match.ToString());

            }

        }

        Console.WriteLine(String.Join(",", results));

    }

}