To chase an enemy, you could say "pursue the enemy" or "follow the enemy." Here are a few examples of how you might use these phrases in a sentence:

"We need to pursue the enemy before they escape."
"The enemy is on the run, we must follow them."
"I'll take a small team and pursue the enemy while the rest of you hold the fort."

It's worth noting that "chasing" or "pursuing" someone can sometimes have negative connotations, particularly if it's done in a threatening or aggressive way. If you're chasing someone in a miptary or law enforcement context, it's important to follow rules of engagement and use appropriate force.