Don't worry about it too much. People are busy shopping, working overtime, not playing on the web during December.
Yes, there is fall in traffic because of holidays but for gifts & online shopping sites, traffic & visitors increasing
this is expected in the month of December. So wait for new year when all people came back from holidays and start their work on computer.
It depends on the niche. Sites such as gifts and online stores will do well while some others may experience a decrease in visitors. Just as in real world where some shops will do well while others won't.
Even my sites experienced a decline in Traffic by 20%. But I have noticed the same thing last year as well. I feel that New Year celebrations would also have a huge impact on my website traffic.
At Christmas time website traffic was very slow because of holidays..But for gifts & online shopping sites, traffic & visitors increasing.