Summarize this article in one sentence.
Have the bike's serial number ready to give them if you know it. You can do this online, but showing up in person at the nearest police station may lead to a faster response. Let the police know about your GPS tracker if one is attached to your bike. There are many websites that keep a local or global registry of stolen bikes. You can enter information about your theft on these for free. Let your friends know that your bike is stolen, post about it on social media, and tell people who spend time near where it was stolen (such as the employees at the business you locked your bike in front of). The more people who know your bike was missing, the greater the chance someone will see it and tell you. Be sure to provide your contact information and a detailed description of your bicycle. Craigslist and other online noticeboards often have sections for announcing stolen bikes. If you receive information, pass it on to police. Return to the spot your bike was stolen and look at nearby buildings for video cameras. If you see any, ask the owners if you or the police can review their tapes to help identify the bike thief. eBay, Gumtree, and Craigslist are all common places for bike thieves to sell bikes. Check regularly for bikes of the model that was stolen for bikes that might be yours. If you find a likely candidate, notify the police and the website owners. The easiest way to do this is to set up an automatic alert on each site that will send you an email every time a bike of a certain model is put up for sale. The process varies for each website; search the FAQ or ask customer service about "automatic alerts", "auto-search", or "saved searches". Find out where used bikes are commonly sold in your area and visit them. If you see your bike there, make sure it's yours and contact the police. Bicycle theft is covered under some plans, but you'll need to submit the claim within a certain time period following the theft. If you used a high-security lock, contact the manufacturers and see if they have an anti-theft guarantee. Once you've located your bike, let the police recover it rather than risking injury to do so yourself.

Summary:
File a police report as soon as possible. List your bike as stolen in an online database. Spread the word. Post stolen bike notices on telephone poles and online. Ask for surveillance tapes, if available. Keep an eye out for similar bikes sold online. Visit local flea markets and other places secondhand bikes are sold. File a claim with your renter or homeowner insurance. Do not take risks to recover the bike yourself.