Cambridge police are looking for a young man wanted in connection with a knifepoint robbery that occurred Thursday night on Trowbridge Street.

The victim said a teenager on a BMX bike approached him and demanded his money. The victim surrendered his $30, police said, and the robber fled toward Kirkland Street.

The suspect was described as black, about 18 years old and 5 feet, 9 inches tall, with a stocky build, wearing a beige or brown coat. Two other robberies occurred last week around Hampshire Street in which the suspect had a similar description and method of operation, although police have not said there is any connection.

In other police news:

— A city man was charged yesterday with assault and battery on a person over the age of 60 or who is disabled. Dennis Splaine, of 70 Richdale Ave., stuck his finger in an old man’s eye and bit him on the arm, leaving the elderly victim with a bloodshot eye, welts and bite marks, police said.

— Police responded to a complaint yesterday from the pastor of the Adventist Congregational Church at 171 Hampshire St., who said someone used a brick to shatter the side windows of the church — one of more than 30 incidents of vandalism that occurred in the past week, including tires being slashed and car windows smashed on Normandy Avenue, as well as Charles, Third and Thorndike streets.