A prelude: I don't have easy access to all of them Dragon magazine electronicals, so this is just from the paper books - the Player's Handbook, unless otherwise noted.
Sending is useful for speaking to someone when you don't know exactly where they are. It's a level 6 ritual; simpler rituals like Animal Messenger require you to have a location in mind. Sending has a limited range in miles unless you can hit a 40+ ritual Arcana check, though, so you might need to be in the center of the continent or sweep across it, and you don't actually know if you've reached someone with it unless they decide to answer you.
Animal Messenger is only active for a few hours depending on your check, so if you can find someone you need to be within a small distance to contact them - though if you can follow the animal you can use it as a rough guide for direction.
The definitive answer, Observe Creature, will definitely let you see them in particular and where they are, as long as it's on the same plane, but it's level 24. You don't need to be level 24, you could just obtain a scroll, which would work at any level, but you would need a viewing glass of some sort worth 10,000 gp.
For something slightly easier, if you know something that you suspect they may still have on them, View Object is a level 18 ritual that will let you observe the area around any object you know of anywhere on the same plane, though you'll need to pick something that would also be somewhere you could actually see useful location details from - a favorite dress, say, might just stay in a wardrobe for the brief window of time you have to look around. The viewing glass in this case only needs to be worth 1,000 gp.
Lastly, if they exist somewhere there's a map of, Magic Map is a level 9 ritual from Arcane Power that lets you find someone on a map, given that you have "an object tied to them", like a lock of hair. The map itself has to be at most 50 miles square, though, so depending on where they are a sufficiently detailed map of their location might not exist. You'll only need to sink another 100 gp into a divining rod or plumb of some sort for this one.