I've looked around and everyone assumes so, but I see no specific mention that imps have hands (with which to wield wands to cast spells for their masters, as familiars).
It is safe to say, "Yes, they have hands."
According to the PFSRD:
Imps vary widely in appearance, ranging through a spectrum of bestial traits and grotesque body shapes, though most take the forms of red-skinned, winged humanoids with bulbous features. Such a typical imp stands a mere 2 feet tall, has a 3-foot wingspan, and weighs 10 pounds.
Humanoid shapes could imply hands.
- According to the Paizo website's picture of an Imp Familiar, they are shown to have hands - and even holding a scroll.
Here is another picture of a Pathfinder Imp (and as MrLemon pointed out in comments regarding the Bestiary - it clearly has hands):
© 2009, Paizo Publishing, LLC
Artist credit: Adam Vehige
Print source: Christopher Self (2009). The Asmodeus Mirage, Paizo Publishing, LLC.
Web source: Joshua J. Frost. (February 5, 2009). The Monsers of Adam Vehige, Paizo Blog.
Most depictions of imps do have hands.
However, when you consider to have an imp as a familiar for a player-character through the arcane bond class feature, I would not recommend to allow it to use equipment as this might become quite unbalanced.
From a balance POV, familiars are supposed to be weak. Imps are already far stronger than most vanilla familiars. But when you additionally allow it to wield magic weapons and even wands in combat, they can become far more powerful than intended. And that for classes which usually are already considered quite overpowered.
When you want to have a more balanced imp companion, you can summon one as a Lesser Planar Ally which is a 4th level spell. Imps are one of the weaker choices for this spell, so powering it up with equipment would not be too unbalanced.
Another option is to arrange that an imp agrees to cooperate with the party on its own accord and joins the party as a GM-controlled NPC. When it is under the GMs control, then anything goes. But in that case the imp will completely retain free will, so it will likely only pretend to be the trusty servant of the player characters while following its own, likely very malicious, agenda.