Okay, so recently in my game a large piece of a building came crumbling down on a couple of civilians and I only had an action to try to prevent it. Unfortunately, I really didn't have any spells that could stop it but I did have the spell command. I commanded them to 'run' since they were all frozen in fear and it worked for all but one of them. Really sad. My question is, can you all think of any other way I could have done this? I was thinking maybe I could have cast summon celestial and asked the DM if he could have a shield to deflect the debris.

I am playing a high-level Twilight Cleric currently, but I'd also like to hear suggestions if I had a different build. Like if I had magic initiate and took a certain spell from a different list it would have been useful or maybe a certain magic item would be relevant. 

Clerics are super powerful, specially Twilight, but indeed they lack the versatility to handle this situation you exposed — this is the niche of a Wizard, who would be able to prevent this through Wall of Force.

• An upcast of Aid could give them enough HP to survive the collapse
• If they were within your movement speed and close enough together you could cast word of recall. (Assuming you have prepared a sanctuary, this is a good spell to have prepared to get the party out of Dodge if things go belly up). They might end up on a different continent but at least they are still alive.
• At a pinch you could use plane shift if you have a fork attuned to smewhere that wouldn't instantly kill them
• You could roll the dice with divine intervention if available
• If all else fails you have revivify

• If you have a spell gem put TIny Hut inside it, then you can cast it as an action instead of 1 minute.
• Banish the civilians if you have the spell slots to up-cast it enough to get all of them.
• If it came at an angle (like down a hill) Blade Barrier might work, but it is specifically a vertical wall.
• Control Water: Redirect Flow to smash into the wall and push it out of the way?
• Etherealness at 8th level lets you take 3 willing creatures with you into the Ethereal plane.
• Gate would work if you have 9th level spells.
• You could try to get your DM to let you cast Stone Shape on it to swiss cheese it so that it falls around you Buster Keaton style. If I were a DM I might allow this if you succeed on a Dex check, since you have to touch the stone, so would need to get the spell cast before you're crushed to the ground.

First, let me say that use of command was really good thinking. 
As far as stopping it, my first thought was telekinesis, since I’m pretty sure I’ve seen every Jedi ever do something similar, second was levitation. Maybe haste so you could run in, grab them and pull them out. None of those are really options for you, I’m realizing, sorry about that if it’s not useful, just those spells seem the obvious choices. There are some magic items that can allow you to cast those spells though, ring of telekinesis in particular.