The most recent blaze broke out at about 2:45 Tuesday morning at the Classy Nails Salon in the Laurelwood Plaza on the 600 block of Blackwood Clementon Road.
Investigators say this fire does not appear to be accidental.
"We have an arson-detection dog, we did find some evidence of an accelerant used. We took samples and we sent it to the state police lab for an analysis," said Deputy Chief Fire Marshal Paul Sandrock.
The first fire happened early Sunday morning. That was limited to the exterior of the nail salon. However, Monday's fire gutted the salon and several other businesses sustained smoke and water damage.
Police are looking at two surveillance cameras mounted on a nearby building for clues.
No one has been injured in the fires.
There is no word yet on any suspects.