Most stores were closed but Americans still managed to shop on Christmas Day -- increasingly on their smartphones.

An IBM survey showed Christmas Day online sales were up 16.5 percent over last year, with a strong boost from smartphones and tablets.

Mobile traffic was the highest IBM found over this holiday season, accounting for 48 percent of all online traffic. And mobile accounted for nearly 29 percent of all online sales, up 40 percent over 2012.

Smartphones drove 28.5 percent of all online traffic compared to 18.1 percent for tablets, according to IBM. But tablets drove twice as many sales -- 19.4 percent of all online sales, to 9.3 percent for smartphones.

Tablet users averaged $95.61 per order, versus $85.11 for smartphone users.

IBM found that Apple iPhone and iPad users were bigger shoppers than their counterparts using Google Android-powered devices

As a percentage of total online sales, Apple's iOS was more than five times higher than Android, driving 23 percent of sales to 4.6 percent for Android.

On average, iOS users spent $93.94 per order, to $48.10 per order for Android, according to the survey.

Shoppers referred from Facebook averaged $72.01 per order, while Pinterest referrals drove $86.83 per order, IBM said. However, Facebook referrals converted sales at nearly four times the rate of Pinterest referrals, the report found.