Google's parent company Alphabet on Thursday posted lower profit and a small revenue increase for last year's fourth quarter, as a decline in online ad spending and competition from rivals weigh on the search giant.

While overall revenue grew, advertising revenue fell by nearly 4% and revenue at YouTube declined 8% year-over-year. That appeared to spook investors, who sent the company's stock lower in after-hours trading.

The Mountain View, California-based company said it earned $13.62 billion, or $1.05 per share, in the October-December quarter. That's down 34% from $20.64 billion, or $1.53 per share, in the same period a year earlier.

Revenue inched 1% higher to $76.05 billion from $75.33 billion.

Analysts expected Alphabet to post earnings of $1.18 per share on revenue of $76.2 billion for period, according to FactSet Research.

Shares in Alphabet Inc. fell $4.55, or 4.2%, to $103.19 in extended trading.