I had a very similar experience last year with a girl that suddenly went missing from the group.
in our situation, we first tried calling her on cellphone and walkies. we didn't hear her so we stationed her best friend and one of the weaker skiers at the lift she had to take to wait for her to come out on her own. Meanwhile we went back up to the spot where we had last seen her and followed potential skitracks that could belong to her. we did this in groups of 2 and every group had walkies, cellphones. we slowly made our way down, calling out her name and listening but didn't find her. Since our first own search was unfruitful we informed the mountain rescue and they coordinated a search with us. We gave them detailed descriptions of her, where we were going and where we last saw her. Her best friend who was the most shook was kept sidelined with a liftie who had contact with skipatrol. The rest of us cooperated with the patrols/rescueworkers of the resort , they split our group of +-10 skiers up into 3 groups and divided us among their own experienced rescuers, we then searched the area in groups of 4-5 skiers, skiing down some potential tracks, spread out on a line, within sight/shouting distance and slowly made our way down the mountain.
in the end, after about an hour of organized searching, it was a group of two lifties/mtn rescuers that found her. Apparently she took a wrong turn and ended up in on a gnarly face and tried to ski her way down and out of it but it only got more hairy.... she fell and bruised a leg and got stuck behind a tree... Later we heard from herself that she took a completely different turn and traversed our initial run, she got to a lift and tried to find us again by going back up but she was actually heading to the other side of the resort, she got off the lift and panicked, she tried to make her way back to where we were and without knowing it, she skied down this gnarly face, she kept going lower and lower in the hope it would become easier but it didnt :/
in the end she got airlifted by a rescue helicopter but luckily she was quite ok!
That whole ordeal of 3-4hours between beginning to feel something is wrong and seeing her face to face again was definitely one of the most terrifying and exhilarating ski-experiences i've ever had !