Christopher, a 45-year-old from St. David's, disappeared early on June 1st.
However, the mystery truly began in the days beforehand, as police and family members say Christopher was acting strange.
"He was acting somewhat irrationally in the days prior to his disappearance but we do not believe it was a psychiatric or mental health emergency," said Sgt. Andrew Block of the Radnor Twp. Police Dept. during a news conference on Tuesday afternoon.
His sister, Sylana Christopher, went into more detail during a recent interview with Action News. She said, when Gerald came to see his mother on Memorial Day, he was fine.
However, she told Action News that Gerald went to a barbecue that day, held by a client, and became very fearful. He shook a woman's hand and started to panic, saying he had seen her before.
"He kept on telling his fiancee that he had to leave, that he had to go. He got in the car and left her there," said Sylana Christopher, who added that the woman was known to the man who hosted the barbecue.
Sylana said the family learned that Gerald went to a park and was there for three hours. He went home that night and taught a class at the gym on Tuesday, but was said to be quiet.
Sylana also said that Gerald told his fiancee several times on Tuesday that someone was following him and wanted to kill him. His fiancee believed he was having a panic attack, Sylana said, and Gerald became agitated before going to bed on Tuesday night.
Between Tuesday night and Wednesday morning he left and no one has seen him since.
"We later found out he took his bike from his gym and left his ID, all of his credit cards, money, everything was all left behind," Sylana said.
Sgt. Block went on to say that police are not aware of any activity on any of Christopher's financial accounts.
Christopher is described as a black male, 6 feet 4 inches tall with a muscular build. He was possibly wearing dark-colored shorts and black sneakers with yellow stripes when he left early on June 1st. He may also be operating a black and yellow sport racing bike.
Investigators say there are no signs of foul play in this case.
Anyone with more information should contact Radnor Police at 610-688-0503.
There is also a Facebook page set up in hopes of finding Gerald Christopher.
