Speaking as a lawyer, you clearly have at least a decent cause of action against either the landlord or your friend. Surely the landlord has a right to cut the locks (and maybe sell the bike) if he provides reasonable notice. But I would argue that notice was per se not reasonable simply based on the fact that your friend never received it.

Talk to the landlord and demand compensation. If he refuses, file a claim in small claims court (it's very cheap and relatively easy to do). He'll be forced to either take the time (and maybe money) to defend or you'll get a default judgment against him. At the very least, you should be able to recover the amount he made for selling the bike (unjust enrichment), but I'd argue for the full cost of a replacement.