It's extremely liberating to tell people.
When you keep it a secret, you're telling yourself, "I should be ashamed that I have this". And then you start to feel the shame. But you shouldn't because you did not choose to have social phobia. Certain circumstances and probably genetics chose for you. You should never, ever feel ashamed of something that was put upon you against your free will.
Shame is honestly one of the most difficult emotions to cope with and often causes depression. If you trust anyone, anyone at all, you should tell them. Let go of that nasty emotion. SA is not a part of your identity, it is something you are suffering from, like the flu. Don't treat it as part of your identity. Let it go.