Yousuf was described by police as being about 5ft 6ins (1.7m) tall and he wore glasses.
He was last seen wearing a Lyle and Scott grey hoodie, North Face trousers and black trainers.
Meanwhile, Muhammad was described as being about 4ft 7ins (1.4m) tall and he wore square glasses.
He was last seen wearing a black hoodie, grey tracksuit bottoms and black trainers with a white stripe, according to West Yorkshire Police.
Det Insp Dicorato said: “We are carrying out extensive inquiries to find them.
“We would like to hear from anyone who has seen them or who has any information that could assist.”
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