A penny stock may spike if there is a buzz around it, for example, if users on Reddit or some other platform are talking about it. In other cases, if a bigger company is contemplating acquiring the company that the penny stock represents, this may lead to its demand, and hence, price hike. Sometimes, an influencer like a billionaire investor dropping a tweet on the penny stock may also lead to amateur investors picking it.
That said, a sudden spike may be followed by a steep decline in the price of a penny stock, which mandates extreme caution. It may be better to rely on a stock's fundamentals like the company's products/services and its market share before making any investment decision.