The search resumed on Monday for the missing father and son from Minnesota who disappeared while hiking in Colorado.

Damian McManus, 51, and Evan McManus, 18, drove from St. Louis Park, Minn., to Echo Lake in Colorado, as part of a spring break trip, a family spokeswoman told Minneapolis ABC affiliate KSTP. They were last accounted for on Wednesday, when the elder McManus phoned his wife and daughter, who were on their own spring break trip in Mexico.  

A search for the missing McManuses on Sunday turned up no leads, according to the Denver Post. The search, which focused on Echo Lake’s Mount Evans, consisted of about 20 rescuers who were assisted by a helicopter. Rescue efforts ended Sunday afternoon due to bad weather.

Searchers were unsure exactly where the father and son hikers went missing, a spokesman for the Alpine Rescue Team told the Post.

"Anyone who is familiar with Echo Lake knows it is rather sizable," said Bill Barwick. "There's a number of different trails they could have taken."

The missing McManuses were supposed to be back in Minnesota over the weekend, according to Minneapolis NBC affiliate KARE. The separate trips were supposed to be bonding experiences. Katherine McManus, the elder McManus’ wife and Evan’s mother, said she hadn’t heard from her husband and son since Wednesday, but she wasn’t concerned at the time because the area where they were hiking had spotty cell phone service. She became alarmed on Sunday after she returned from Mexico with her daughter and Evan’s twin sister, Lauren McManus.

"We became really worried when we got off the plane from Mexico [Sunday] afternoon and she still hadn't heard anything from Damian, we tried texting them and calling them and both of their phones were dead," the family spokeswoman, Andrea Bouzara, told KARE.

A Facebook group, “Missing: Damian and Evan McManus,” was created to spread awareness of the missing father and son hikers.  Evan McManus’ girlfriend, Ashley Ritten, said she exchanged texts with Evan McManus on Wednesday. She speculated that either the father or son is seriously injured and the other is staying close by.

“He is going to be okay," she said. "They know that you can't leave one person if they are injured, and if they are lost off-trail they are staying out waiting for us to get them,” she said. “The weather is being kind to them and warming up, and they have plenty of water from the snow. Thinking what-ifs is not going to help, just please stay positive. Evan and Damian would not want us to be falling apart, they just want us to find them.”

Family and friends are hoping that anyone who last had contact with the McManuses can come forward. They said Damian McManus may stand out because he has a British accent. Financial records showed the father and son dined at a Denny’s in Lakewood, Colo., on Wednesday.