What about Wechat? There are lots of seemingly pretty girls trying to voice or video call these days. Either I'm suddenly rich in their eyes or there's something fishy going on.
Name a chat app and I can provide a link or comment from someone saying the same thing about pretty scam girls. Facebook, Whatspp, Gmail, Kik, Snapchat, Instagram, and even BBSes, AOL, IRC etc...
What I saw on FB is automatic replies from bots. What I know from Skype are african boys who try to earn their next beer in an internet cafe by acting they would be a girl. I can confirm it's all not that.