The hashtags #PrayforParis and #JeSuisCharlie were among the top 10 news trends cited by Twitter for 2015, referring to the deadly November 13 rampage in the French capital and the killings at the Charlie Hebdo magazine on January 7.

Meanwhile, the #BlackLivesMatter message came to represent a social movement, becoming a rallying cry for social justice after killings by police of blacks in cities including Ferguson, Missouri and Baltimore, Maryland.

But the most-retweeted single message was about the British pop band One Direction.

US President Barack Obama's tweet following the Supreme Court's affirmation of gay marriage, using the #LoveWins hashtag, was another widely-viewed message, retweeted some 448,000 times. And Saudi King Salman's message of prayer and support to his people shortly after inheriting power was retweeted 368,000 times.

The most used news hashtags were #jobs, #Quran and #ISIS while the top technology themes were #iPad, #SoundCloud and #Android.

The stars most talked about on Twitter were American singer Ariana Grande, Argentine singer Oriana Sabatini and Mexican actress-singer Dulce Maria.