using System;

using System.Collections.Generic;

using System.Linq;

​

public class Contact 

{

    public int ContactId { get; set; }

    public String Name { get; set; }    

}

public class Program

{

    public static void Main()

    {

        var test = new List<Contact> { 

            new Contact { ContactId = 1, Name = "Fulano" },

            new Contact { ContactId = 2, Name = "Beltrano" },

            new Contact { ContactId = 3, Name = "Ciclano" }

        };

        var test2 = test.FirstOrDefault(x => x.GetType().GetProperty("ContactId").GetValue(x).ToString() == 1.ToString());

        Console.WriteLine(test2.Name);

    }

}