Four Oklahoma friends were reported missing on Monday after they did not return from a bike ride.

Mark Chastain, 32; Billy Chastain, 30; Mike Sparks, 32; and Alex Stevens, 29, of Okmulgee, were reported missing Monday evening. Mark Chastain's wife, Jessica, and Alex Stevens' mother reported their disappearances.

"I know nothing, and I'm feeling lost. I'm heartbroken. I'm sad. I have so many mixed emotions and thoughts," Jessica Chastain told Fox News Digital. "As far as I know, nothing has been recovered. Nothing has been found. There is no sign of foul play."

Okmuglee police believe the four "close friends" left Billy Chastain's home on the west side on Okmuglee for a bike ride on Sunday evening. Two of the men had their cell phones with them, but attempts to call them went straight to voicemail, according to police.

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Jessica Chastain said it was typical of her husband and his friends to go on bike rides, and he would not have left without a trace. He was supposed to watch their two children on Monday morning, when she started a new job.

Investigators on Wednesday gathered video and GPS evidence and followed up on potential sightings of the men — including one witness who reported seeing all four men walking down the street at 2 a.m. Tuesday.

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Investigators are working to confirm the sightings but only have witness descriptions as of Wednesday.

"This evening and tomorrow we will begin the long and tedious process of sifting through the hours of video as well as the GPS data," the Okmulgee Police Department said in a Wednesday Facebook post. "Additional locations have been identified as potential sources for more video and they will be contacted tomorrow. Search warrants have been submitted for phone records and warrants for Facebook accounts will be forthcoming."

Okmulgee YMCA

A witness purportedly spotted two of the missing men outside an Okmulgee YMCA on Monday. (Google Maps)

One witness claimed to have spotted Alex Stevens by himself on Sunday around 4 p.m. outside the Okmulgee Indian Community Smoke Shop, or the "Smoke Shop," on the south side of Okmulgee. Another witness purportedly spotted Mark and Billy Chastain on Monday near a YMCA. 

Authorities have been tracking the men's cell phone data and established a path of where they might be but have so far been unable to locate any sign of the four friends. 

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Jessica said her husband's phone pinged last around 5:24 p.m. Sunday. All she wants is to "bring them home."

"Although there is no evidence to indicate violence or any foul play at this point, a small contingent from the District 25 Violent Crime Task Force is assisting, which allows us to bring more resources to bear in the search," the Olkmulgee Police Department said Tuesday.