Traveling from Malaga to algarve

I would check from Sevilla, but it's likely a bit of a slog.
Are they going to rent a car once there? You might want to share their entire itinerary and you'll get more detailed solutions.

As you are finding, public transport links between Spain and Portugal aren’t as good as you might expect.

There are no direct flights from Malaga to Faro.

Getting from Madrid to the Algarve will take all day. The best route would be Malaga to Seville with a change in Córdoba by train then a bus from Seville to Faro. Alternatively, you can travel all the way by bus with a change in Seville. It’s going to take most of the day door to door.

Whereabouts on the Algarve are they heading? Most places particularly in the west are best by car, so I would suggest hiring a car in Faro.

Thanks for the replies! They are flying from NYC to Madrid and visiting a friend near Malaga for a few days before heading to Portugal. They do not have any set itinerary yet (any recommendations would be awesome) but they have two weeks. They wanted Lisbon and Porto will Algarve be too much to fit in if they are already using 3 of the days visiting their friend in Spain?

Thanks for the replies! They are flying from NYC to Madrid and
visiting a friend near Malaga for a few days before heading to
Portugal. They do not have any set itinerary yet (any recommendations
would be awesome) but they have two weeks. They wanted Lisbon and
Porto will Algarve be too much to fit in if they are already using 3
of the days visiting their friend in Spain?

Are they flying home from Portugal or Spain? I ask because they may need/want a car in the area anyway, and if they are returning to Spain, it makes sense to drive. If departing from Portugal, they need to return the car in Spain to avoid hefty fees, and so car won't help.
Are they spending time in Madrid before heading to Malaga?
Have they traveled in Spain before, do they wish to? Or is it just a stopover to visit the friend in Malaga?

In addition to the excellent advice above, suggest you stop speaking in generalities about "days" they have to spend. Get specific about how many actual, full days on the ground they will have in Spain/Portugal (best to provide actual dates), and do not count their arrival or departure days as usable, plus specify which/how many days they already have committed to visit one place or another. Without that kind of specific detail, it's very easy to tell yourself little white lies about how much time you really have, which in turn makes it really easy to load up an unrealistic and wasteful itinerary which will not be enjoyable (and might not even be doable).

Getting between parts of Spain and parts of Portugal often turns out to be a lot less convenient and more time consuming than most first-time visitors expect. You may be looking at one of those situations, so be careful in your expectations and planning.

You don’t say how long the trip is - I think the Algarve, Lisbon, Porto and the wonderful towns between Lisbon and Porto needs the best part of 3 weeks to do it justice.