do you know any good sites for two girls who are starting the process of finding a third person for the first time ever?

I am not an expert in online dating since I have never done it, but I know lots of poly folk have had good luck on OKCupid. You could also try the subreddit r/polyamory and poly forums, like the Poly Forums and Polyamory Online. I don’t belong to any of these forums, though, so I don’t know their community policy on things like personal ads, nor can I actually recommend them.

You should also consider using the internet to find local poly meetups - the best directory for that is here.

Faithful readers, help me help these girls! Where have you had luck meeting other poly folk online?