Unfortunately, searing doesn't actually lock in juices; in fact it's been shown to take out slightly more juice than just baking, most likely because the meat is exposed to a higher heat during the sear which causes more evaporation. You can read slightly more about it on the wiki for Searing and a lot more about it in this previous thread. In fact, when you hear the constant sizzle in the pan as you pan fry, that's juices coming out and onto the pan. You can verify this by searing one side, searing the other, then flipping it again - you'll see juices seeping out through the seared side.
However, you do still want to sear meats whenever possible. Through the Maillard reaction you'll get a much more complex flavor that can't be matched through baking alone.
Most likely, my guess is that you're baking the salmon too long which is causing it to dry out. Are you wrapping it in a pouch with some liquids when you cook it? That can help a lot if you're baking but isn't absolutely necessary by any means. With or without a pouch, make sure that you're serving it pretty much right after pulling it from the oven - it will continue to cook after you remove it, whether you use a pouch or not.
You can also try reducing the time and increasing the heat a little bit and see if that helps at all. You want to be sure to keep the skin on if possible - this contains a lot of fat, which will help keep from drying out. I generally bake with the skin-side up so the fat can render down through the fish as it bakes.
You can find a great Good Eats episode about pouch cooking on YouTube, the first part of the episode can be found here. I generally don't follow recipes for pouch cooking - once you get a feel for it you can eyeball it with what you have around - but a good start might be this recipe.
Poaching the fish after searing is another good technique, and very easy, but be careful - although it's not common sense, you can still dry things out by poaching. Some people think poaching is error-proof and will just throw food in water and leave it until they're ready to eat it - this will result in dry meat.
The best way to cook salmon is to grill it over a high heat. even better if you can get a cedar plank to put it on. Oil the fish (or the grill, your choice) lightly and cook it for a few minutes (4-6) on each side, depending on how thick the fish is. You can tell when it's done because it will be fully opaque and flake easily with a fork. Keep a watchful eye - once salmon is close to being done, it will become overdone fast, so you want to pull it from the heat as early as you can without undercooking it.