To make it more clear, this broadcaster is not someone speaking over a microphone, it's just someone using their cellphone to broadcast a live session to viewers. Ideas?
A broadcaster is generally someone, or something, that distributes, relays, transmits a message to someone, or something, else.
The translation provided by Google Translator for "broadcaster" is "locutor de rádio", which is a very specific type of broadcasting, for radio.
However, you can find more meaningful translations for "broadcast" such as "transmissão" (transmission, to transmit) or "difundir" (to propagate).
So the broadcaster is the "transmissor" or "emissor" as @Jacinto suggested.
Both "broadcast" and "broadcasting" can also be used as foreign words, they are even accepted without the use of quotation marks. This usually happens when foreign words are adopted as is to another language, due to relatively high usage.
1Pensaste em emissor? Não sei porquê, soa-me melhor. Jan 12, 2017 at 10:17
@Jacinto Parece ser uma boa escolha também. Jan 12, 2017 at 10:30
Pá, inclui. Isto assim em abstrato é um bocado difícil: as palavras em frases tomam sentidos mais precisos. Mas de maneira geral, vejo uma pessoa mais como emissor do que transmissor; transmissor faz-me lembrar mais equipamento. Jan 12, 2017 at 10:34
1@Jacinto Mas eu editei a resposta, depois de fazer o comentário xD Jan 12, 2017 at 10:40
Não tinha visto :) Jan 12, 2017 at 10:42
I would use "divulgador". The verb "divulgar" means to spread information or ideas to a large public, in any form, verbal, written or visual. "Difundir" can also be used, but the derivated noun "difusor" can be confused with something that difuses a substance in another one. "Divulgador" leaves no doubt.