why when i start demo server in s2 alpha 0.5x nobody can find it ????

That's because you are using an outdated version of LFS. You have to upgrade to the demo versjon Z28 to see the servers online atm

If you want others to see/connect to your 0.5X server - everyone should have a compatible patch (your friends wouldn't see your patch X server with with a LFS Z28 version).

And...

Quote from shiny_red_cobra :

[...] the master server supports patches as old as patch V. ATM there is 1 V server and 2 W servers, and a bunch of X and X10 servers.