All Bitcoin transactions are public, traceable, and permanently stored in the Bitcoin network. Anyone can see the balance and transactions associated with any address.
Listed below are some online tools that can help with tracking Bitcoin transactions. Researcher Brenna Smith wrote an article explaining how to use all these tools together to perform an investigation.
Blockexplorer is a tool that gives you access to the public ledger of various digital assets including Bitcoin.
BitcoinWhosWho is a tool that allows to look up the history of Bitcoin addresses. The information is crowd-sourced, so use with some skepticism.
WalletExplorer is a tool is similar to the Blockexplorer (above). However this service goes a step further because it reveals other addresses that are in the same Bitcoin wallet. It can also reveal if the Bitcoin was transferred from a particular exchange.
You can also do a simple search engine query on a Bitcoin addresses — this may lead you to a webpage connected to the address.
Photo credit: Karsten Winegeart