The name Iu is predominately used within Catalan-speaking countries / territories that are either Catalan-speaking, or are included in larger political units where Catalan is the official, co-official or semi-official language, such as Andorra, the autonomous communities of Spain which include Catalonia, the Balearic Islands (Mallorca, Menorca, Ibiza and Formentera), the Valencian Community, Aragon (in La Franja) and Murcia (in Carche), Northern Catalonia (a historical region of Catalonia in Southern France), and the city of L'Alguer in the Italian island of Sardinia.
In Catalan-speaking countries / territories, the name Iu is both a one and two-syllable name, pronounced either EEoo (similar to the English digraph 'ew' within the words 'new' and 'few'), or EE-oo. The form Ïu is only pronounced EE-oo.
Though Iu is a classic Catalan name, it's not normally found among general personal name sites, and glad to see it here, as it's my personal favourite for a boy / male. It doesn't quite translate well in English, yet along with the name Ivo, the name Hugh (though a different origin) makes a good transliteration.