New videos have emerged showing missing Mollie Tibbetts smiling and laughing with her friends the day before she vanished.

The University of Iowa student was last seen going for an evening jog in Brooklyn, Iowa, where she was staying in her out-of-town boyfriend's home, on July 18.

The 20-year-old was reported missing the following day when she didn't turn up for work.

Her father Rob Tibbetts has directly appealed to her kidnapper to 'let Mollie go' and 'turn yourself in.'

And as the search for the young woman continues, a friend shared videos of the carefree student and issued a plea for tips.

One of the clips, taken the day before she vanished according to ABC News, shows a giggling Mollie sitting cross-legged on the floor as a friend records her - while the other shows her salsa dancing in a gym.

In the first clip, she is seen laughing as the camera zooms in before lifting a small mirror to cover her mouth then sticking her tongue out.

Mollie Tibbetts vanished on July 18 while out on an evening jog. Friends have now shared last videos of the student before she disappeared in a bid to urge witnesses to come forward

Jarrett Rose shared the two clips of Mollie on Facebook, writing: '2 weeks since I've seen your smile and it feels like an eternity has passed by.

'Your voice echoes through my heart every day, giving me the inspiration to never give up on you. No one has, or ever will give up hope and stop searching for you!

'NO TIP IS INSIGNIFICANT!!! Please contact the tip lines if anyone knows anything! We WILL bring you home Mollie, and you'll be salsa dancing in no time!'

Meanwhile, Mollie's father told Fox News on Tuesday that his daughter didn't just 'get up and walk away,' so it's logical to assume she has been abducted.

He said: 'To that person, you're probably very afraid. This isn't probably a situation that you anticipated.

'You don't know how to extricate yourself from this but the best thing to do at this point is to put an end to it...'

In a new video shared by friends of missing Mollie Tibbetts before she vanished, she is shown giggling sitting cross-legged on the floor

In another clip shared by friends a laughing Tibbetts is seen salsa dancing in a gym

'Do not escalate this and do not miss out one more day. Let Mollie go and turn yourself in.'

Mollie's father previously said he believes there is someone out there with information that could help located his missing daughter.

'It doesn't matter what we're going through, we just need people to think – because somebody knows something, and they don't even know it's important,' he said.

Mollie's father Rob Tibbetts (above) believes there is someone out there with information that could help located his missing daughter

He also said on Monday night that he feels his daughter is with someone she knows who is now 'in over their head'.

'If someone out there is holding Mollie, and they're in over their head and they've made a horrible mistake, you can end it now before it goes any further,' he said at a press conference.

Later, he said he was encouraged by the fact they had not found her body.

'I'll be honest with you early on I wasn't as hopeful as I am now.

'The longer we go without finding Mollie's body the more hopeful we are that she's alive somewhere and going through something that she can survive.'

But while her father is hopeful, Mollie's mother says she is in 'purgatory' and is tortured by her daughter's disappearance.

''I'm either going to be headed up to heaven or down to hell, depending on the result,' Laura Calderwood, told DailyMail.com last week.

Meanwhile, police say they are looking at surveillance footage from businesses along the route Mollie usually jogs.

The data from Mollie's Fitbit, which contained GPS-enabled tracking, is also being analyzed.

University of Iowa student Mollie Tibbetts was last seen going for a jog in Brooklyn, Iowa, on July 18

But they revealed no specific details about developments in the case at a press conference on Monday.

On Monday, it was revealed that a pig farmer questioned by FBI agents over the disappearance had refused to take a polygraph test.

Wayne Cheney, 56, who lives in a trailer in Guernsey around 10 miles from Brooklyn, appeared on the radar of authorities after a red shirt similar to Mollie's daycare center uniform was found in a field near his home.

However, it is not clear if it the shirt actually belonged to Mollie or not.

Cheney, who has previous convictions for stalking an ex-girlfriend, has spoken three times to police.

He has also given interviews where he laughs nervously and says he had no idea where Mollie is, but suspects 'some guy has her'.

When the FBI asked him to take a polygraph test, he refused.

'I don't need to. It's stupid,' he told The Des Moines Register on Monday.

He has allowed police to search his home and land, saying he had 'nothing to hide.'

Mollie (pictured with her boyfriend Dalton Jack) was reported missing on July 19 when she didn't show up for work. Her boyfriend was working out of town and she was staying in his home

Mollie was staying overnight at her boyfriend Dalton Jack's home with his dogs when she vanished.

Dalton was ruled out early on as a suspect because he was working 130 miles away in Dubuque at the time.

His brother and his brother's fiancée who also live in the home were also cleared because they had alibis.

Meanwhile, the reward fund for information on Mollie's disappearance has now exceeded $300,000.

Greg Willey, spokesman for Crime Stoppers of Central Iowa, says the Mollie Tibbetts reward fund has reached $301,363, which is a record for the organization that was incorporated in 1982.

Willey says donations have come from more than 180 individuals and businesses from across the country.

Wayne Cheney (pictured) has been questioned about Mollie's disappearance, but refused to take a polygraph test

Officers from the FBI, state and local law enforcement agencies are working to find her.

She was last seen jogging in her home town of Brooklyn, which has a population of 1,400, and is located around 70 miles east of Des Moines.

On Sunday, a body of a young woman was found in rural Lee County near West Point in southeast Iowa, around 87 miles from where Mollie was last seen.

But authorities later said the body was not Mollie.

Special Agent Rick Rahn, of the Iowa Criminal Investigation Division, said on Monday that investigators identified the body as that of another 20-year-old woman, Sadie Alvarado, who lived in Muscatine.

Rahn says a 28-year-old man has been charged with leaving the scene of a fatal accident in connection to Alvarado's death.