Robbers targeted 'vulnerable' victims at Meadowhall Interchange and in Poole Road, Darnall, Sheffield, on Sunday night.
Investigations into both incidents are underway.
A police spokesman said: "Please make sure you keep your belongings safe and yourself even safer. Be aware of the people around you and help us to help you.
"Don't have your mobile phone on show or advertise any of your flashy electronics. Don't make it easy for them.
"Thieves have no respect for you, themselves or your property."
Csll South Yorkshire Police on 101.