Yesterday I lost my mobile phone. I accidentally left it on the train and somebody took it. When I sent a message to it they threw my phone away. I reported it to the police and it reminded me that sometimes you might need to report lost property to the police.
Speak formally, but simply
You should start with “I’d like to report” then a noun.
If somebody took something of yours that thing was stolen. If you left it somewhere and can’t find it, it was lost or it is missing. We often talk about missing persons as well.
Examples:
“I’d like to report a stolen wallet.”
“I’d like to report a lost phone.”
“I’d like to report a missing coat.”
Anticipate the questions
You will be asked questions about the item’s appearance. There is a useful post about colours here, one about shapes here, and another post about patterns.
“What does it look like?”
I’d describe the colour and/or pattern, and the shape.
“How big is it?”
Compare the size to something ordinary or use your hands to show a size and say “This big.”
“When did you last have it?”
Answer using the day and time.
Example dialogue:
“I’d like to report a missing bag, please.”
“Certainly. When did you last have it?”
“Um, at about quarter past one this afternoon.”
“Thank you. What does it look like?”
“It’s an olive green shoulder bag with a black zip.”
“How big is it?”
“Oh, it’s about the size of a laptop computer but a bit fatter.”
“Thank you. Could you fill in this form, please.”