The general rule of thumb is that if you don’t look like Brad Pitt, you probably don’t attract the ones that look like Scarlett Johanssen… Unless you have great personality or are a multi-billionaire, or a very powerful government official (or two of those three…)
I assume the trick he is using in his profile that attracted the women was not posting his (recent) photo.
But seriously - yes, it is a scam. If it were not, he’d have an actual address, phone number etc. plus details like where she works, among other things. (trouble is, those can be actually traced. What are the odds these women are even in the alleged country of origin? Odds they are real?) tell him to ask for Skype video call, see what excuses they come up with.
Absolute best case is they are looking for a green card. What’s the current process for that? BTW, once a foreigner with limited means, assuming they even ever get a visa (unlikely) as soon as they tell the CBP they are coming into the USA to meet their fiancée, they risk being deported on the theory they are planning to marry without a green card and then not leave. I’ve read several sites where people suggest that even telling the customs people you have a boyfriend, fiancée (or husband) means they’ll never get a tourist admission to the USA until the green card comes through, a timeline measured in years or longer…
Best case.
Worst case, yes, they’ll scam someone for all their money, there is no Maria or Louisa or whoever, it’s some clever scammer anywhere in the world of indeterminate gender, with a friend/contact in South America to handle the money end of things.
How do you fix this? You don’t. My favorite saying is - “You can lead a horse to water, but you can’t make it think.” You can’t even beat sense into it with a 2x4.
At the very least, tell him that there’s no point in paying for a plane ticket until they have a visa. There’s no way a bribe is necessary or accepted in any consulate or embassy of the USA (if he says there is - call the State Department) and local officials who take bribes have nothing to do with the USA visa, so his financial contribution should be limited to the visa fee (what, $100 or something) until it is approved. Get her to send a picture of the visa and he can probably ask his local border control to check if it is real.
But then, if he’s that far gone he’ll fall for the sick mother routine anyway and send medical funds… (Tell him to ask for a photo of her and her sick mother… I bet not many modelling sites have that. It will be photoshopped…)