I’ve never met a [name_f]Thea[/name_f] [name_m]IRL[/name_m]. Like pps, I would pronounce it thee-ah (soft th- like in “with”) unless corrected. I think it would be a perfect sister-name with [name_f]Viola[/name_f]!
[name_f]Thea[/name_f] and [name_f]Viola[/name_f] are nice together, but it would be pronounced thee-uh all the time (at least in [name_u]America[/name_u]). I’ve never met one before.
I have never met a little [name_f]Thea[/name_f]. I think that the they-a pronunciation won’t come naturally to most people at most glance. I think it goes very well with [name_f]Viola[/name_f]!
It popped into the top 100 here in 2016, but it’s back out again (we don’t have data below the top 100).
I know a couple of Theas, but they’re adults. All pronounce it Thee-uh (with a soft ‘th’).
I think it can work as a nickname for [name_f]Anthea[/name_f], [name_f]Althea[/name_f], [name_f]Theodora[/name_f] etc, but it’s fine on its own too. It works well with [name_f]Viola[/name_f].