They all (almost all) do escorting (and under escort I mean prostitution).
Honestly, this idea that all pornstars do escort is in my opinion, vastly exagerated. Of course the statistics are hard to find, but just take a look at the girls on the first page of Woodman Castings or EBI and try to find the ones who do escort.
I would say that, at best 15% do escort and that's really generous. If I count honestly, it's less than 10%.
And for most of them, it's only really escort in the classical sense, which means being advertised through an agency for about 500€/2h local and more than 1500€/day abroad. How many meetings do they get per month through this ? 2 at best ?
A small part of the porngirls do tours through a bunch of website in Paris/London/Dubai/Athens, but it's always the same 15-20 girls.
And about 40 of them occasionaly spend a week in a studio in Germany/Swiss/Austria. And occasionaly means one to 5 times a year. And here also the market is pretty small, since I count about 5 to 8 studios with regular pornstars compared to the hundreds of escort studios in those countries.
An interesting point is that if you go to a forum dedicated to prostitution, you'll notice that only a fraction of punters are interested in pornstars. Most of them say that those girls are too artificial or the price is too high.
So as much as I stand by to the idea that porn can lead to prostitution because it's a natural escaladation process, I would add that the numbers say that most porn girls don't go into prostitution.