Sry for the multipost, hope it's not confusing. I've got some Hamachi instructions here.
For starters, Hamachi is a great Virtual LAN creator. It simulates a network over the internet, making your computer think everyone connected is on the same network, even though they are not. Anywho...
[link=http://filehippo.com/download_hamachi/]Download Hamachi Here[/link]. Go through the tutorial, its short and cuts down on confusion. Any and everyone that wants to play must have it (MAX 16 ppl with free version)
Have the host enter sv_lan 0 and heartbeat just as a fail safe in the console.
Then when you want your friends to join have them go into console and enter: connect YOURHAMACHIIP:27015
NOTE: Your hamachi IP WILL NOT be your normal IP that you think you know, it will however be found in big bold letters at the top of the program.
So, quick check:
-Is Hamachi allowed through your firewall?
-Is TF2 allowed through your firewall?
-Is TF2 fully updated?
-Is Hamachi the same version?
-Is the host IP address you are giving people your Hamachi IP?
-Is sv_lan 0 in place? <-- 0 = ZERO not the letter
-Did the host enter 'heartbeat' upon creating the server?
If this doesn't work then I'm sorry I have failed you, but I'm for now out of options and must get back to studying.
If they do work, then have fun!