(So, I would think either Investigation or Survival to look for tracks or clues.  I'll go with Investigation if that's OK)

Blackberry also searches the area for any evidence of what happened or where the culprit or Elk Running may have escaped to.

Investigation 26 (game log)

Blackberry finds a disturbance in the snow across the street from Tond's cabin and tracks leading between the houses toward the woods on the edge of town.

The harengon administers one of the herbal tonics to Naraeld, while he alerts his other two companions to the tracks.

As the magical potion works it's way into his body, the worst of Naraeld's wounds start to close up and it is mere heartbeats until he takes a sudden breath, before jerkily rolling himself over and coughing up blood onto the cold floor. For the second time tonight Naraeld comes to his senses feeling groggy and pained, to see the friendly, furry face of Blackberry. "We really must stop meeting like this." Though his voice is croaky and his breathing laboured there is a warmth in his tone and a grimaced smile full of thanks. "You seem to have saved me from the precipice twice now my friend, I am again in your debt once more."

Struggling to get himself up, noting the pool of his own blood as he does so, Naraeld sees Sabetha and Aubin also in the hut. Upon hearing Blackberry's recounting of the tracks outside, Naraeld confirms their suspicions. "Sephek bested me and stole Elk Running away. We must give chase." He shakily picks up his stave from where it had fallen... where he had fallen. Then he heads out of the hut and tries to identify the tracks. His sense of urgency and desperation are clearly blinding him to his dire state of health, yet he stumbles on.

"Good to see you among the living Naraeld. Now lets find Sephek" says Aubin. He will then do his best to follow the tracks.

Survival Check

8

The expressionless look which now seems permanently affixed to Sabetha's pale face softens for the briefest moment as she simply nods "Naraeld" in acknowledgement as her companion arises.  Her scarf remains pitch dark as he confirms her suspicion about Sephek Kaltro.

"Sephek disappeared from where he had been helping set things right in Mead Hall, leaving behind a small, perfect ice sculpture of an Elk which Blackberry found.  A sculpture much like Elk Running herself told of seeing, much larger, in the visions that the Frostmaiden invaded her dreams with."

Sabetha trots outside and begins following the tracks Blackberry had found with unnerving determination.

Survival:  27 (Natural 20)

Blackberry hops along after the others, shaking his head ruefully.  "All four of us are just barely alive.  One good hit to any of us and back down we go.  This is not well thought out," he mutters to himself, and the frosted buildings as he passes them by.

Based on the tracks you find, you believe that Sephek is only a few minutes ahead of you. He seems to be headed to the edge of town. With him holding Elk Running, it seems likely the party will quickly catch him 

Sabetha answers Blackberry grimly, her teeth set and her mouth flat.  Eyes flicking from the tracks to her surroundings and back rapidly.

"You are right, Blackberry.  But how can we let him carry Elk Running off after almost murdering Naraeld?  In cold blood (literally).  My thought is that we try to kill him at range.  I with my longbow, you three with your magic.  I will admit I am not thinking straight, though.  What say you all?"

She suggests everyone keep their eyes open to watch for Sephek so we can attack at a distance, following suit herself.

Perception:  24

In particular, Sabetha wants to make sure Sephek any of his allies do not double back to take them unaware, hoping to get multiple shots off before that.

Naraeld grimly nods his acknowledgements to Aubin and Sabetha. Blackberry's summation that they are only minutes behind their quarry reassures the big half-breed, a glimmer of hope that his failure has not been absolute. Taking stock of the hunting party's state though Naraeld suddenly realises their number has diminished, fearing bad news he ventures the question, "Where are Greth and Eva? Tell me they are not lost to the raiders? I remember them giving chase after I left the hall but lost track as we took different paths."

Naraeld moves with the group, his actions gradually becoming easier and more fluid as his body benefits from the last of the herbal tonic. "I can't argue that I'd rather have a rematch with the odds stacked more favourably, yet to let Sephek get away with Elk Running is something we cannot allow. There is more to the tale, and I will share it later should time allow, for now though, I must keep Elk Running from Auril's grip, we must get her back to Bryn Shander, and that means rescuing her from Sephek. Arrows and magic are well and good but I would not want to risk hitting Elk Running."

"I hate to suggest splitting up, but you are the fastest of us, 'Betha, and likely also faster than Sephek, who is burdened with dragging or carrying our friend's body.  You should try circling around him and blocking his escape while we catch up from behind.  But that is dangerous, you will be alone for a short while until we arrive."

Greth finishes restringing his bow, then acknowledges Eva's suggestion. "I do not need them to track the others, and would not trust them to lead us anywhere. Surrender them to those inside, as they should decide the fate of those who attacked the town. Not us. Once delivered, we must move to keep pace. They will likely meet up, then split up again. If what she says is true, the leaders won't be able to maintain control of their band. There will be no incentive to keep the children, and releasing them may be their only hope of avoiding being hunted by every community."

"I understand your feeling Blackberry, but if we wait until we are fully healed then we will assuredly lose Sephek." says Aubin as he follows along

Eva acknowledges Greth'g'karee's words with a nod. And yet, she has paid a price. Torn, Eva averts her gaze from the girl: "If you persist in refusing to hand yourself over, I shall not force you. However—and I warn you once—you are not to follow us. You are on your own, Mallifyr."

“Nodum maleficarum,” Eva says as she traces a sigil in the air. “Tutela me circumda.” The sigil dissolves, its energy enveloping her in a blue translucence before fading. [She casts mage armor on herself, making her AC 17 for 8 hrs.]

And then she lights the old, rusty lantern. "Lead the way, goliath."

@LtG

What would you like me to roll to track them?

"Oh, I don't want to lose Sephek either," replies the harengon as they follow the trail.  "But the three of you were until recently all unconscious, and I only escaped the same fate by the smallest of my whiskers.  We have but one healing potion left among us. What good does it do to find the murderer, if with a few lucky strokes of his blade, we all lay at his feet bleeding out?  Adding our four corpses to his trophy case does nothing to avenge our friend or bring justice to the Ten Towns."

"And what will we do if we let him go. I doubt he is going to stick to trade routes. If we don't get him here than I don't foresee finding him anytime soon. Meandering through the wilderness with no leads or direction would take too long. It is too urgent of task to me and I will not let this go. Not when we are so close" says Aubin. He hurries along the tracks in hopes of catching up to Sephek.

Eva considers the goliath's indifference. A part of her admires his clarity and singlemindedness; another part is confused by how much his morality differs from Sabetha's or Naraeld's.

The goliath is not burdened by emotions, as Sabetha is, nor by the written laws and conventions of the sedentary inhabitants of Icewind Dale.

Which approach is right?

Ruefully Naraeald nods his agreement with Aubin. "I am in no better state than when Sephek and I faced of a moment ago. He will not be an easy target... tougher than Duhk, much tougher in our present state. However, we cannot let him escape with Elk Running; the consequences would be severe. If I can get his attention, he will stop fleeing. He will want to finish the job he started at Tond's. I can guaruntee that. Perhaps that would give the three of you a chance to lay an ambush, or maybe recover Elk Running whilst Sepheknis distracted and get her to safety. The other option is to track, but not engage. See what he does and maybe an opportunity will present itself." 

Greth'g'karee and Eva:

 Everybody else: