Translation:The party continues since last night.
If I was actually at the party and said to someone "the party started last night" that would be a fair translation I guess. Obviously context is everything.
The accepted version "The party continues since last night" sounds a bit odd and maybe "continues since" is better as "continues from" or even "carries on from". Oh well, the lesson, as always, is to try to be as literal as possible and then curse when you are caught out :-)