Police Scotland is urging the public to be cautious when selling valuables online and to keep details of your location to a minimum to avoid attracting thieves.
Following several incidents of acquisitive crime in the North East, officers believe some perpetrators are using information on buy and sell sites to find and target potential victims.
Detective Sergeant Bruce Buntain said: "Selling valuables online like cars or bikes can be a quick and easy way to make money, and the majority of people using sites like Gumtree are legitimately looking for a good deal.
"However there is often a risk involved when posting your details on the Internet and, in this case, flagging up to the wrong people what you are selling and where you might be keeping it.
"I would urge the public to be cautious when it comes to posting specific information about your location online so that you don't tip off potential thieves. My advice would be to keep your location as general as possible and provide more information to legitimate buyers once you've made contact.
"Police in the North East are using every resource available to us to tackle opportunistic crimes, however it's important we all do what we can to ensure thieves don't stand a chance in the first place.
"It's never too late to make your home security a priority to make it impossible for these people to gain access to your valuables. The most simple thing you can do is ensure your doors are always locked, including any vehicles, even when you are at home.
"Some perpetrators simply try front and back doors in the hope they are open and grab any keys or valuables lying nearby. It might also be worth considering putting in additional security measures like security lights and robust locks to put them off.
"If you have noticed any suspicious activity where you live please let us know as soon as possible. Look out for unfamiliar people and most importantly, tell us.
"Anyone with information should contact Police on 999 if it is an emergency, on 101, or Crimestoppers on 0800 555111 if you would prefer to remain anonymous."