Tho and altho, shortened forms of the conjunctions though and although, have each had a few brief heydays scattered through the history of modern English, but neither has permanently caught on. This could change in the coming years as Textish makes such shortened words more common. For now, though, edited publications prefer though and although to tho and altho, and the shortened forms might be considered out of place in formal writing.
Tho and altho often appear in informal writing on the web—for example:
Seriously tho – this is a now a Left Wing v Wrong thing! [comment on Guardian]
Altho I also belive she was humiliated when they switched her team … [comment on Us Magazine]
Yeah You Cute and The Whole 9, But Can You Cook Tho????? [posted on Twitter]
But edited publications tend to use the longer forms—for example: